Which of the following equals 20?

Question

Accepted Answer

1. Expand: $(\sqrt{13}+\sqrt{7})^2=13+7+2\sqrt{91}=20+2\sqrt{91}.$
2. Subtract: $20+2\sqrt{91}-2\sqrt{91}=20.$
3. Quick checks: (a) $(\sqrt8+\sqrt2)^2-4\sqrt{16}=18-16=2.$
4. (b) and (c) are not 20: (b) $=20+2\sqrt{99}$, (c) $=10+8\sqrt{6}.$
5. Thus the correct choice is **(d)**.

FINAL_ANSWER: d

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Answer

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