Bellringer

Write and equation for each graphBellringer

5-5

Direct Variation

Direct Variation

A function in the form ,where

, is a direct variation. The constant of variation, , is the coefficient of . The variables and are said to vary directly with each other.

k

kxy

yx

0k

x

Is it direct variation?

To discover this, just solve for y. Find the constant of variation

x5 x5xy 52

2

5k

xy2

5

2

025 yx

2

Is it direct variation?

Try these please. Remember: To discover this, just solve for y.

843 xy 925 yxxy 27

yes no no

Write the equation from a point

Given point: (4, -3)

44

kxy 43 k

4

3k

xy4

3

Write the equation from a point

Your turn!Point (-3, -6)

Point (12, -8)

Direct Variation Tables

Use the ratio, , to tell whether y varies directly with x.

Why? Since, k =

If yes, then write the direct variation equation.

x

y

x

y

x y

-2 1

4 -2

8 -4

-10 5

Assignment

Page 264Numbers: 2-28 even