The square of x is expressed as x²
y varies directly, so:
y ∝ x²
Make into an equation by introducing k, the constant of variation:
y = k x x²
y = kx²
To find k, use the condition given x = 2 when y = 12
k = y/x²
k = 12/4
k = 3
Thus y = 3x²
y = 3x5²
y = 75
