A 2 b 2 2abc July 8, 2019 16 32 64 128 A 2 b 2 2abcosθ A^2 ×b^2 + 2ab cos A 2 b 2 2abcosθ proof A 2 b 2 c 2 2abc A 2 b 2 c 2 2abc 1 Sqrt(a^2 + b^2 - 2abcos theta) Root a 2 b 2 2abcos Root a^2 + b^2 + 2abcos theta R 2 a 2 b 2 2abcos Under root a 2 b 2 2abcostheta Prove that c 2 a 2 b 2 2abcosc
