For any real number x, y, f (x + y) + F (X-Y) = 2F (x) cosy, f (0) = 0, f (π / 2) = 1 (2) Proof: F (x) is an odd function and a periodic function

Prove: from F (x + y) + F (X-Y) = 2F (x) cosy, f (0 + y) + F (0-y) = 2F (0) cosy = 0. From F (x + y) + F (X-Y) = 2F (x) cosy, f (x + π / 2) + F (x - π / 2) = 2F (x) cos π / 2 = 0

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1. Given a = 1 / 2x ^ 2y-1 / 3xy, B = 3xy + 2 / 3Y ^ 2. Find a + B and a-b
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