The triangle whose three sides are 2n2 + 2n, 2n + 1, 2n2 + 2n + 1 (n is a positive integer) is () A. Acute triangle B. right triangle C. pure triangle D. acute or right triangle

∵ (2n2 + 2n) 2 + (2n + 1) 2 = 4n4 + 4n2 + 8n3 + 4n2 + 4N + 1 = 4n4 + 8n3 + 8n2 + 1; (2n2 + 2n + 1) 2 = (2n2 + 2n + 1) (2n2 + 2n + 1) = 4n4 + 8n3 + 8n2 + 1; (2n2 + 2n) 2 + (2n + 1) 2 = (2n2 + 2n + 1) 2, the ∵ triangle is right triangle, so choose B

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