Question

If f(x) = х2 – 2x and g(x) = 6х +4, for which vаluе оf x does (f + g)(x) = 0?

Answer 1

Answer:

$\boxed{\text{x = -2}}$

Step-by-step explanation:

ƒ(x) = x² - 2x

g(x) = 6x + 4

(f + g)(x) = x² - 2x + 6x + 4 = x² + 4x + 4  

$\begin{array}{rcr}x^{2} + 4x + 4 & = & 0\\(x + 2)^{2} & = & 0\\x+2 & = & 0\\x & = & \mathbf{-2}\\\end{array}$

$(f + g)(x) = 0 \text{ when } \boxed{\textbf{x = -2}}$

Check:

$\begin{array}{rcl}(-2)^{2} + 4(-2) + 4 & = & 0\\4 - 8 + 4 & = & 0\\0 & = & 0\\\end{array}$

OK.

Answer 2

Answer:

x = - 2

Step-by-step explanation:

(f + g)(x) = f(x) + g(x)

f(x) + g(x) = x² - 2x + 6x + 4 = x² + 4x + 4

Equating to zero, that is

x² + 4x + 4 = 0 ← left side is a perfect square

(x + 2)² = 0, thus

x + 2 = 0 ⇒ x = - 2