Question

If f(x) = x^2 - 2x and g(x) = 6x + 4, for what value of x does (f + g)(x) = 0?

Answer 1

x = -3 + √5 and x = -3 - √5

Explanation:

Combine f and g:

f = x^2 -2x

+g = 6x + 4

-------------------------

(f + g)(x) = x^2 + 6x + 4

Set this result = to 0 and solve for x:

By completing the square, we get:

y = x^2 + 6x + 9 - 9 + 4, or

y = (x + 3)^2 - 5 = 0

Thus, (x + 3)^2 = 5, and:

x + 3 = ±√5, or

x = -3 + √5 and x = -3 - √5

Answer 2

x = -2

Explanation:

`f(x) =x^2 -2x\:\: and \:\: g(x) = 6x + 4\\(f+g)(x) = f(x) + g(x) \\(f+g)(x) = x^2 -2x+ 6x + 4\\(f+g)(x) = x^2+4x + 4\\(f+g)(x) = (x+2)^2\\ 0 = (x+2)^2...[\because (f+g)(x) =0]\\0 = x+2\\\therefore x = -2`