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If [tex]f(x)=x^2 - 2x[/tex] and [tex]g(x)=6x + 4[/tex], for which value of [tex]x[/tex] does [tex](f+g)(x) = 0[/tex]?

A. [tex]-4[/tex]
B. [tex]-2[/tex]
C. [tex]2[/tex]
D. [tex]4[/tex]


Sagot :

To find the value of [tex]\( x \)[/tex] for which [tex]\((f + g)(x) = 0\)[/tex], we first need to understand the given functions [tex]\( f(x) \)[/tex] and [tex]\( g(x) \)[/tex].

Given:
[tex]\[ f(x) = x^2 - 2x \][/tex]
[tex]\[ g(x) = 6x + 4 \][/tex]

The function [tex]\((f + g)(x)\)[/tex] is simply the sum of [tex]\( f(x) \)[/tex] and [tex]\( g(x) \)[/tex]:
[tex]\[ (f + g)(x) = f(x) + g(x) \][/tex]

Now, let's substitute [tex]\( f(x) \)[/tex] and [tex]\( g(x) \)[/tex] into this equation:
[tex]\[ (f + g)(x) = (x^2 - 2x) + (6x + 4) \][/tex]

Combine like terms:
[tex]\[ (f + g)(x) = x^2 - 2x + 6x + 4 \][/tex]
[tex]\[ (f + g)(x) = x^2 + 4x + 4 \][/tex]

We are looking for the value of [tex]\( x \)[/tex] that makes this expression equal to zero:
[tex]\[ x^2 + 4x + 4 = 0 \][/tex]

This is a quadratic equation. To solve it, we can either factor it, complete the square, or use the quadratic formula. Let’s factor it:

The quadratic expression [tex]\( x^2 + 4x + 4 \)[/tex] can be factored as:
[tex]\[ (x + 2)^2 = 0 \][/tex]

To find the roots, we set the factor equal to zero:
[tex]\[ (x + 2)^2 = 0 \][/tex]
[tex]\[ x + 2 = 0 \][/tex]
[tex]\[ x = -2 \][/tex]

Therefore, the value of [tex]\( x \)[/tex] that satisfies [tex]\((f + g)(x) = 0\)[/tex] is:
[tex]\[ x = -2 \][/tex]

Thus, the correct value of [tex]\( x \)[/tex] is [tex]\(-2\)[/tex].