Write the quadratic variation equation for the relationship: y varies directly with x2 and y = 36 when x = 3.

A. y = ¼x^2

B. y = 12x

C. y = 4x^2

D. y = x^2 + 25

The answer is C. y = 4x^2

y varies directly with x2 can be expressed as:

y = k*x ²

When x = 3, they y = 36. And you just need to replace it in the equation from above:

36 = k*3²

36 = k*9

⇒ k = 36/9 = 4

So, the related equation is

y = 4x²