Question

If y varies directly as the x^2 and y = 200 when x = 5, what is the value of y when x = -3?

a.
-72
b.
120
c.
72
d.
-120


Please select the best answer from the choices provided

Answer 1

As the variation is direct we have:

`y = kx ^ 2`
We must find the value of k.
For this, we use the following data:
y = 200 when x = 5
Substituting values we have:

`200 = k5 ^ 2`
Clearing k:

`k = 200/5 ^ 2 k = 200/25 k = 8`
Then, the function is:

`y = 8x ^ 2`
We evaluate the function for x = -3

`y = 8 (-3) ^ 2 y = 8 (9) y = 72`
Answer:
the value of y when x = -3 is:
c.
72