A b c 2 2abc July 8, 2019 16 32 64 128 A 2 b 2 c 2 2abc 1 A 2 b 2 c 2 2abc formula Cho a 2 b 2 c 2 2abc 1 A 2 b 2 2abc A 2 b 2 2abcosθ A 2 b 2 2abcosθ proof A^2 ×b^2 + 2ab cos
