Mark (√) against the correct answer in the following:
Let f : N → X : f(x) = 4x2 + 12x + 15. Then, f - 1(y) = ?
f(x) = 4x2 + 12x + 15
⇒y = 4x2 + 12x + 15
⇒y = (2x + 3)2 + 6
⇒√(y - 6) = 2x + 3
⇒
f - 1(y) =