9

Set 13: Quadratic Equations (Advanced)

Explanation

Answer: A

Expand: (x+6)(x−6)(x + 6)(x - 6)

A.

x2−36x^2 - 36

✓ Correct
B.

x2+36x^2 + 36

C.

x2−12x−36x^2 - 12x - 36

D.

x2+12x−36x^2 + 12x - 36

Detailed Explanation

Choice A is correct. Choice A is the correct answer. Difference of squares: (x+6)(x−6)=x2−36(x + 6)(x - 6) = x^2 - 36. The middle terms cancel: x2−6x+6x−36=x2−36x^2 - 6 x + 6 x - 36 = x^2 - 36. Choice B is incorrect because the sign should be negative. Choice C is incorrect because middle terms cancel in difference of squares—there's no −12x-12 x term. Choice D is incorrect because middle terms cancel and sign is wrong.

Key Steps:

•

The correct answer is x2−36x^2 - 36

Why others are wrong:
B: Choice B is incorrect and may result from a calculation error.
C: Choice C is incorrect and may result from a calculation error.
D: Choice D is incorrect and may result from a calculation error.
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