Chabot Mathematics §3.1 Relative Extrema Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu Chabot College Mathematics 1 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Review § 2.6 Any QUESTIONS About • §2.6 → Implicit Differentiation Any QUESTIONS About HomeWork • §2.6 → HW-12 Chabot College Mathematics 2 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx §3.1 Learning Goals Discuss increasing and decreasing functions Define critical points and relative extrema Use the first derivative test to study relative extrema and sketch graphs Chabot College Mathematics 3 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Increasing & Decreasing Values A function f is INcreasing if whenever a<b, then: f (a) < f (b) • INcreasing is Moving UP from Left→Right A function f is DEcreasing if whenever a<b, then: f (a ) f (b) • DEcreasing is Moving DOWN from Left→Right Chabot College Mathematics 4 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Inc & Dec Values Graphically MTH15 • Bruce Mayer, PE 7 DEcreasing 6 5 4 y = f(x) 3 2 INcreasing 1 0 -1 -2 -3 -4 XY f cnGraph6x6BlueGreenBkGndTemplate1306.m 0 1 Chabot College Mathematics 5 2 3 4 5 x 6 7 8 9 10 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Inc & Dec with Derivative df If for every c on f ' (c) the interval [a,b] dx 0 x c • That is, the Slope is POSITIVE Then f is INcreasing on [a,b] If for every c on f ' (c) df dx the interval [a,b] 0 x c • That is, the Slope is NEGATIVE Then f is DEcreasing on [a,b] Chabot College Mathematics 6 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Inc & Dec y f x x 3 4 2 The function, y = f(x),is decreasing on [−2,3] and increasing on [3,8] Chabot College Mathematics 7 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Inc & Dec Profit The default list price of p(x) =10 a small bookstore’s paperbacks Follows this Formula • Where – x ≡ The Estimated Sales Volume in No. Books – p ≡ The Book Selling-Price in $/book The bookstore buys paperbacks for $1 each, and has daily overhead of $50 Chabot College Mathematics 8 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx x Example Inc & Dec Profit For this Situation Find: • Find the profit as a function of x • intervals of increase and decrease for the Profit Function SOLUTION Profit is the difference of revenue and cost, so first determine the revenue as a function of x: ( ) Rx x px = x × 10 - x 10 x x 3 / 2 Chabot College Mathematics 9 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Inc & Dec Profit And now cost as a function of x: Cx variable cost fixed cost 1x 50 Then the Profit is the Revenue minus the Costs: Px Rx Cx = (10x - x 3/2 ) - ( x + 50) = 9x - x 3/2 - 50. Chabot College Mathematics 10 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Inc & Dec Profit Now we turn to determining the intervals of increase and decrease. 3/2 The graph of the profit y = 9x - x - 50 function is shown next on the interval [0,100] (where the price and quantity demanded are both non-negative). Chabot College Mathematics 11 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Inc & Dec Profit From the Plot Observe that The profit function appears to be increasing until some sales level below 40, and then decreasing thereafter. Although a graph is informative, we turn to calculus to determine the y = 9x - x 3/2 - 50 exact intervals Chabot College Mathematics 12 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Inc & Dec Profit We know that if the derivative of a function is POSITIVE on an open interval, the function is INCREASING on that interval. Similarly, if the derivative is negative, the function is decreasing So first compute the P' x d 9 x x 3 / 2 50 dx derivative, or Slope, 3 1/ 2 function: 9 x 2 Chabot College Mathematics 13 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Inc & Dec Profit On Increasing intervals the Slope is POSTIVE or NonNegative dP 3 1/ 2 9 x 0 so in this case need dx 2 Solving 3 1/ 2 3 1/ 2 9 x 0 x 9 This 2 2 InEquality: 2 1/ 2 x 36 x 9 The profit 3 function is DEcreasing on the interval [36,100] Chabot College Mathematics 14 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Relative Extrema (Max & Min) A relative maximum of a function f is located at a value M such that f(x) ≤ f(M) for all values of x on an interval a<M<b A relative minimum of a function f is located at a value m such that f(x) ≥ f(m) for all values of x on an interval a<m<b Chabot College Mathematics 15 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Peaks & Valleys Extrema is precise math terminology for MTH15 • Bruce Mayer, PE Both of 4 • The Bottom of a Trough, That is a VALLEY 3 2 y = f(x) • The TOP of a Hill; that is, a PEAK PEAK PEAK VALLEY 1 0 -1 -2 -3 0 VALLEY 10 20 30 x Chabot College Mathematics 16 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx 40 50 MTH15 • Bruce Mayer, PE 4 3 y = f(x) 2 Rel&Abs Max& Min Absolute Max Relative Max Relative Min 1 0 -1 -2 -3 0 Absolute Min 10 Chabot College Mathematics 17 20 30 x 40 50 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Critical Points Let c be a value in the domain of f Then c is a Critical Point If, and only if df dx 0 OR x c HORIZONTAL slope at c Chabot College Mathematics 18 df dx x c VERTICAL slope at c Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Critical Points GeoMetrically Horizontal Vertical MTH15 • Zero Critical-Pt MTH15 • Critical-Pt 1.3 20 1 0.9 16 14 y = f(x) 1.1 y=f(x) 18 (0.1695, 1.2597) 1.2 12 10 8 6 0.8 4 0.7 2 0.6 0.05 0.1 0.15 x Chabot College Mathematics 19 0.2 0.25 0 0 0.5 1 1.5 2 x Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx 2.5 3 20 BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx MATLAB Code % Bruce Mayer, PE % MTH-15 • 07Jul13 % XYfcnGraph6x6BlueGreenBkGndTemplate1306.m % clear; clc; % The Limits xmin = 0; xmax = 0.27; ymin =0; ymax = 1.3; % The FUNCTION x = linspace(xmin,xmax,1000); y1 = x.*(12-10*x-100*x.^2); % % The Max Condition [yHi,I] = max(y1); xHi = x(I); y2 = yHi*ones(1,length(x)); % The ZERO Lines zxh = [xmin xmax]; zyh = [0 0]; zxv = [0 0]; zyv = [ymin ymax]; % % the 6x6 Plot axes; set(gca,'FontSize',12); whitebg([0.8 1 1]); % Chg Plot BackGround to Blue-Green plot(x,y1, 'LineWidth', 5),axis([.05 xmax .6 ymax]),... grid, xlabel('\fontsize{14}x'), ylabel('\fontsize{14}y=f(x)'),... title(['\fontsize{16}MTH15 • Zero Critical-Pt',]),... annotation('textbox',[.15 .05 .0 .1], 'FitBoxToText', 'on', 'EdgeColor', 'none', 'String', ' ','FontSize',7) hold on plot(x,y2, '-- m', xHi,yHi, 'd r', 'MarkerSize', 10,'MarkerFaceColor', 'r', 'LineWidth', 2) set(gca,'XTick',[xmin:.05:xmax]); set(gca,'YTick',[ymin:.1:ymax]) Bruce Mayer, PE Chabot holdCollege off Mathematics Chabot College Mathematics 21 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx MATLAB Code % Bruce Mayer, PE % MTH-15 • 23Jun13 % XYfcnGraph6x6BlueGreenBkGndTemplate1306.m % ref: % % The Limits xmin = 0; xmax = 3; ymin = 0; ymax = 20; % The FUNCTION x = linspace(xmin,1.99,1000); y = -1./(x-2); % % The ZERO Lines zxh = [xmin xmax]; zyh = [0 0]; zxv = [0 0]; zyv = [ymin ymax]; % % the 6x6 Plot axes; set(gca,'FontSize',12); whitebg([0.8 1 1]); % Chg Plot BackGround to Blue-Green plot(x,y, 'LineWidth', 4),axis([xmin xmax ymin ymax]),... grid, xlabel('\fontsize{14}x'), ylabel('\fontsize{14}y = f(x)'),... title(['\fontsize{16}MTH15 • \infty Critical-Pt',]),... annotation('textbox',[.51 .05 .0 .1], 'FitBoxToText', 'on', 'EdgeColor', 'none', 'String', ' ','FontSize',7) hold on plot([2 2], [ymin,ymax], '--m', 'LineWidth', 3) set(gca,'XTick',[xmin:0.5:xmax]); set(gca,'YTick',[ymin:2:ymax]) Example Critical Numbers Find all critical numbers and classify them as a relative maximum, relative minimum, or neither for The Function: MTH15 • Bruce Mayer, PE 40 2 f x 4 x 2 x 30 20 y = f(x) 10 0 -10 -20 -30 -40 -10 Chabot College Mathematics 22 XY f cnGraph6x6BlueGreenBkGndTemplate1306.m -8 -6 -4 -2 0 x 2 4 6 8 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx 10 Example Critical Numbers SOLUTION Relative extrema can only take place at critical points (but not necessarily all critical points end up being extrema!) Thus we need to find the critical points of f. In other words, values of x so that df 0 OR dx df UnDefined dx Think Division by Zero Chabot College Mathematics 23 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Critical Numbers For the Zero Critical Point d 2 d 0 f ' ( x) 4 x 2 4 x 2 x 2 dx x dx 0 = 4 + 2 × -2x -3 -4 = -4x -3 -3 1= x x 1 Now need to consider critical points due to the derivative being undefined Chabot College Mathematics 24 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Critical Numbers The Derivative Fcn, f’ = 4 − 4/x3 is undefined when x = 0. However, it is very important to note that 0 cannot be the location of a critical point, because f is also undefined at 0 In other words, no critical point of a function can exist at c if no point on f exists at c Chabot College Mathematics 25 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Critical Numbers Use Direction Diagram to Classify the Critical Point at x = 1 | 1 Calculating the derivative/slope at a test point to the left of 1 (e.g. x = 0.5) find f ' (0.5) 4 4(0.5) 3 28 → f is DEcreasing Similarly for x>1, say 2: f ' (2) 4 4(2) 3 3.5 → f is INcreasing Chabot College Mathematics 26 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Critical Numbers From our Direction Diagram it appears that f has a relative minimum at x = 1. A graph of the function corroborates this assessment. f (x) = 4x + 2 x2 Relative Minimum Chabot College Mathematics 27 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature The average temperature, in degrees Fahrenheit, in an ice cave t hours after 10t 1 midnight is T t 2 modeled by: t t 1 Use the Model to Answer Questions: • At what times was the temperature INcreasing? DEcreasing? • The cave occupants light a camp stove in order to raise the temperature. At what times is the stove turned on and then off? Chabot College Mathematics 28 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature SOLUTION: The Temperature “Changes Direction” before & after a Max or Min (Extrema) • Thus need to find the Critical Points which give the Location of relative Extrema • To find critical points of T, determine values of t such that one these occurs – dT/dt = 0 or – dT/dt → ±∞ (undefined) Chabot College Mathematics 29 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature Taking dT/dt: 2 d 10t 1 dT d 2 T t 2 10t 1t t 1 dt t t 1 dt dt Using the Quotient Rule d d 2 t t 1 10t 1 10t 1 t t 1 dT dt dt 2 2 dt t t 1 2 dT t 2 t 1 10 10t 12t 1 2 2 dt t t 1 Chabot College Mathematics 30 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature Expanding and Simplifying 2 2 2 dT 10t 10t 10 20t 8t 1 10t 2t 11 2 2 2 2 dt t t 1 t t 1 When dT/dt → ∞ 2 2 dT 10t 2t 11 2 t t 1 0 2 dt t 2 t 1 • The denominator being zero causes the derivative to be undefined – however,(t2−t +1)2 is zero exactly when t2−t + 1 is zero, so it results in NO critical values Chabot College Mathematics 31 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature When dT/dt = 0 2 2 10t 2 2t 11 2 2 2 t t 1 0 t t 1 10 t 2t 11 0 2 2 t t 1 Thus Find: 10t 2 2t 11 0 Using the quadratic formula (or a computer algebra system such as MuPAD), find Chabot College Mathematics 32 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature For dT/dt = 0 find: t ≈ −1.15 or t ≈ 0.954 Because T is always continuous (check that the DeNom fcn, (t2−t +1)2 has no real solutions) these are the only two values at which T can change direction Thus Construct a Direction Diagram with Two BreakPoints: • t ≈ −1.15 • t ≈ +0.954 Chabot College Mathematics 33 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature The Direction | | Diagram 1.15 0.954 We test the derivative function in each of the three regions to determine if T is increasing or decreasing. Testing t = −2 dT dt 10 2 2(2) 11 2 t 2 2 2 (2) 1 2 25 49 The negative Slope indicates that T is DEcreasing Chabot College Mathematics 34 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature The Direction | | Diagram 1.15 0.954 Now we test in the second region using 2 t = 0: dT 100 2(0) 11 dt t 0 0 2 (0) 1 2 11 The positive Slope indicates that T is INcreasing Chabot College Mathematics 35 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature The Direction | | Diagram 1.15 0.954 Now we test in the second region using t = 1: dT 2 101 2(1) 11 dt t 1 1 2 (1) 1 2 1 Again the negative Slope indicates that T is DEcreasing Chabot College Mathematics 36 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature The Completed Slope | | Direction-Diagram: 1.15 0.954 We conclude that the function is increasing on the approximate interval (−1.15, 0.954) and decreasing on the intervals (−∞, −1.15) & (0.954, +∞) • It appears that the stove was lit around 10:51pm (1.15 hours before midnight) and turned off around 12:57am (0.95 hours after midnight), since these are the relative extrema of the graph. Chabot College Mathematics 37 • Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Example Evaluating Temperature Graphically Relative Max (Stove OFF) Relative Min (Stove On) Chabot College Mathematics 38 10t 1 T t 2 t t 1 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx MuPAD Plot Code Chabot College Mathematics 39 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx WhiteBoard Work Problems From §3.1 • P40 → Use Calculus to Sketch Graph • Similar to P52 → Sketch df/dx for f(x) Graph at right • P60 → Machine Tool Depreciation Chabot College Mathematics 40 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx All Done for Today Critical (Mach) Number Ernst Mach Chabot College Mathematics 41 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot Mathematics Appendix r s r s r s 2 2 Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu Chabot College Mathematics 42 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 43 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 44 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 45 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 46 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 47 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 48 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 49 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx P3.1-40 Hand Sketch Chabot College Mathematics 50 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx P3.1-40 MuPAD Graph Chabot College Mathematics 51 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx WhiteBd Graphic for P3.1-52 Chabot College Mathematics 52 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 53 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 54 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 55 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 56 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 57 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 58 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 59 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 60 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx P3.1-60 MuPAD Chabot College Mathematics 61 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx Chabot College Mathematics 62 Bruce Mayer, PE BMayer@ChabotCollege.edu • MTH15_Lec-12_sec_3-1_Rel_Extrema_.pptx