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2.5.2 – Writing Equations of Lines Cont’d • Yesterday, we could write equations of lines in a few ways • 1) Given slope and y-intercept (y = mx + b) • 2) Given a graph of a line, determine slope and y-intercept (also write in y = mx + b) • 3) Use point-slope form given any point and slope of a line (y - y1 = m(x - x1)) – Could write in y = mx + b as well if we simplified it • We’ll start off still using point-slope form, but this time in a different scenario • Remember, only need 2 points to represent a line • Now, you will be given two points, and you will need to find an equation of that line 2 points • Using two points, we will; • 1) Find the slope, using the slope formula; y2 y1 m = x x 2 1 • 2) Using any of the two points, write in pointslope form • 3) Simplify as y = mx + b • Example. Write an equation of the line that passes through the points (-2, 3) and (2, -5). • Slope = m = • Point-Slope form; • Slope-Intercept form; • Example. Write an equation of the line that passes through the points (-8, 10) and (-2, 17). • Slope = m = • Point-Slope form; • Slope-Intercept form; Graphically • Similar to yesterday, you can determine the equation of a line graphically, even if we cannot accurately locate the y-intercept • Just find two known points, then • 1) Find the slope using rise/run (counting) • 2) Pick one point, use point-slope formula • Example. Write an equation of the line shown. • Example. Write an equation of the line shown. Parallel/Perpendicular Equations • Recall, we covered parallel and perpendicular lines • What determines if two lines are parallel? • What determines if two lines are perpendicular? • Using given info, we will once again use pointslope form after finding each slope • Example. Write an equation of the line that is parallel to y = 4x – 5 and goes through the point (-1, 3). • Example. Write an equation of the line that is perpendicular to y = 4x – 5 and goes through the point (-1, 3). • • • • • Assignment Pg. 98 24, 34-52 even, 59, 60 Pg. 100 11-13