Write the equation of the quadratic function with roots -2 and 4 and a vertex at (1, 9).

Answer 1

since roots are -2 and 4,
equation must be

y = a(x+2)(x-4)
but (1,9) lies on it, so
9 = a(3)(-3)
a = -1

y = -1(x+2)(x-4)
or
y = -x^2 + 2x + 8
or
y = -(x-1)^2 + 9