正弦定理a/sinA=b/sinB=c/sinC=2R（R在同一个三角形中是恒量,是此三角形外接圆的半径）余弦定理a^2 = b^2 + c^2 - 2·b·c·cosA b^2 = a^2 + c^2 - 2·a·c·cosB c^2 = a^2 + b^2 - 2·a·b·cosC cosC = (a^2 + b...