Advanced Math practice question

Answer: A. x² + 8x + 15

Multiply each term of the first factor by each term of the second: x·x + x·5 + 3·x + 3·5 = x² + 5x + 3x + 15 = x² + 8x + 15.

Why the other answers are wrong

B. x² + 15

You multiplied the first terms and the last terms but skipped the two middle products, 5x and 3x. Those combine to the 8x that's missing.

C. x² + 8x + 8

The middle term is right, but the constant is 3 × 5 = 15, not 3 + 5 = 8. The last terms are multiplied, not added.

D. x² + 15x + 8

The 8 and the 15 are swapped. The constant comes from multiplying 3 × 5 = 15; the x-coefficient comes from adding 3 + 5 = 8.

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