Question

Given the quadratic function f(x) = 9x2 – 36x + 36, find a value of x such that f(x) = 9. (Points : 20)

Answer 1

f(x) = 9x2 – 36x + 36
f(x) = 9

so 9x2 – 36x + 36 = 9

divide eqn with 9

we get, x^2 - 4x + 4 = 1
or x^2 - 4x + 3 = 0

x^2-3x-x+3=0
x(x-3)-1(x-3)=0
(x-1)(x-3)=0

so x-1=0 or x-3=0

so x=1 or x=3

so for x=1 and x=3, f(x)=9