Question

If y varies directly as x^2 and y = 144 when x = 4, what is the value of y when x = -5?

a.
-225
b.
225
c.
180
d.
-180


Please select the best answer from the choices provided

Answer 1

As the variation is direct then we have the following expression:

`y = kx ^ 2`
From here, we clear the value of k.
For this we use the following data:
y = 144 when x = 4
Substituting values:

`144 = k4 ^ 2`
Clearing k we have:

`k = 144/4 ^ 2 k = 144/16 k = 9`
Then, the function is:

`y = 9x ^ 2`
When x = -5 we have:

`y = 9 (-5) ^ 2 y = 9 (25) Y = 225`
Answer:
the value of y when x = -5 is:
b.
225