The quadratic function f(x) has roots of 4 and −6, and it passes through the point (1, 21). What is the vertex form of the equation of f(x)?
a.f(x) = −(x − 1)2 + 25
b.f(x) = −(x + 1)2 + 25
c.f(x) = (x − 1)2 + 25
d.f(x) = (x + 1)2 − 25