Question

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

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