Question

25.) If y varies directly as x, and y = -18 as x = -2, find y for the x-value of 20.

Answer 1

Yo sup??

since y varies directly with x we can say

y=kx

at y=-18, x=-2 then

-18=k*(-2)

k=9

therefore

y=9x

at x=20

y=9*20

=180

Hope this helps.

Answer 2

Answer: the value of y is 180

Explanation:

If y varies directly as x, then as y increases,x increases and as y decreases, x decreases.

We would introduce a constant of proportionality, k. Therefore,

y = kx

When y = - 18, x = - 2

Therefore,

- 18 = - 2 × k

Dividing the left hand side and the right hand side of the equation by

- 2, it becomes

- 2k/ -2 = - 18/-2

k = 9

The expression becomes

y = 9x

Therefore, when x = 20,

y = 9 × 20 = 180