由余弦公式 c^2 = a^2 + b^2 - 2ab cosC = 4; => c = 2(1) 周长为 a + b + c = 5(2) cos(A-C) = cosAcosC + sinAsinC其中cosC = 1/4,sinC = sqrt(1 - cosC^2)cosA = (b^2 + c^2 - a^2) / 2bc; sinA = sqrt(1 - cosA^...