Advanced Math practice question

Answer: A. 3x(x + 4)

Both terms share the factor 3x: 3x² = 3x · x and 12x = 3x · 4. Pulling it out gives 3x(x + 4). Check by expanding: 3x · x + 3x · 4 = 3x² + 12x.

Why the other answers are wrong

B. 3x(x + 12)

After taking 3x out of 12x, what remains is 12x ÷ 3x = 4, not 12. Expanding 3x(x + 12) gives 3x² + 36x.

C. 3(x + 4)

An x was dropped. 3(x + 4) expands to only 3x + 12 — there's no x² term, so it can't equal 3x² + 12x.

D. x(3x + 4)

Only x was factored out, and then the 12 became a 4 without the 3 being taken out to justify it. x(3x + 4) expands to 3x² + 4x.

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