Direct Variation
(section 4.6)
Review of graphing: Graph the line y = 2x - 3
Review: Direct Variation
Two variables, usually x and y show ___________________
when ____________
Compare
y  ax
y  mx  b
.
Slope (m) is the same as _____ called the _________________________
The y-intercept (b) is ________ so this line will go through _________________
Graph these 2 lines on this one coordinate plane:
1.
yx
y-intercept=______
slope = ________
constant of variation =____
2.
1
y x
4
y-intercept=______
slope = ________
constant of variation =____
3.
6 y  12 x
y-intercept=______
slope = ________
constant of variation =____
4. x  3 y  0
y-intercept=______
slope = ________
constant of variation =____
You may also need to determine if a table of values represents a direct variation.
Look at the relationship between y and x in the tables. If the table represents direct variation,
then the ratio of y to x must be true for each ordered pair.
Ex 6) Does the table represent direct variation?
x
-28
-24
-20
12
8
y
-7
-6
-5
3
2
Ex 7) Does the table represent direct variation?
x
10
24
40
60
y
15
30
60
120
Write the direct variation equation then find the y-value:
1) "y varies directly as x". If y = 24 when x =3, find y when x = 10.
2) "y varies directly as x". If y = 5 when x =30, find y when x = 12.
3) "r varies directly as d". If r = 5 when d = 10, find r when d = 15.
The depth of a lake, d, varies directly with r, the amount of rainfall last
month. If a is the constant of variation, which equation represents the
situation?
A. d = ar
B. d = r/a
C. d = a/r
D. d = a + r