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If [tex]$x^2 + mx + m$[/tex] is a perfect-square trinomial, which equation must be true?

A. [tex]$x^2 + mx + m = (x-1)^2$[/tex]
B. [tex][tex]$x^2 + mx + m = (x+1)^2$[/tex][/tex]
C. [tex]$x^2 + mx + m = (x+2)^2$[/tex]
D. [tex]$x^2 + mx + m = (x+4)^2$[/tex]

Sagot :

To determine which of the given equations is a perfect square trinomial of the form [tex]\(x^2 + mx + m\)[/tex], we need to match it to the standard form of a perfect square trinomial, which is [tex]\((x + a)^2 = x^2 + 2ax + a^2\)[/tex].

### Step-by-Step Solution:

1. Compare each option to the form [tex]\((x + a)^2\)[/tex]:

- For [tex]\((x - 1)^2\)[/tex]:
[tex]\[ (x - 1)^2 = x^2 - 2x + 1 \][/tex]
Here, [tex]\(x^2 - 2x + 1\)[/tex]. It does not fit the form [tex]\(x^2 + mx + m\)[/tex].

- For [tex]\((x + 1)^2\)[/tex]:
[tex]\[ (x + 1)^2 = x^2 + 2x + 1 \][/tex]
Here, [tex]\(x^2 + 2x + 1\)[/tex]. It partially fits but does not carry the same coefficient for the middle term and last term.

- For [tex]\((x + 2)^2\)[/tex]:
[tex]\[ (x + 2)^2 = x^2 + 4x + 4 \][/tex]
Here, [tex]\(x^2 + 4x + 4\)[/tex]. It fits the form [tex]\(x^2 + mx + m\)[/tex] perfectly where [tex]\(m = 4\)[/tex].

- For [tex]\((x + 4)^2\)[/tex]:
[tex]\[ (x + 4)^2 = x^2 + 8x + 16 \][/tex]
Here, [tex]\(x^2 + 8x + 16\)[/tex]. It does not fit the form [tex]\(x^2 + mx + m\)[/tex].

2. Find the matching equation:
Among the given options, only [tex]\((x + 2)^2 = x^2 + 4x + 4\)[/tex] fits the needed form of [tex]\(x^2 + mx + m\)[/tex].

Thus, the correct equation must be [tex]\((x + 2)^2\)[/tex], which means:

[tex]\[ x^2 + mx + m = (x + 2)^2 \][/tex]

So, the correct option is:

[tex]\[ \boxed{3} \][/tex]