求函数y=(sinx+cosx)2+2cos2x的最小正周期.
求sin220°+cos250°+sin20°cos50°的值.
当-π/2≤x≤π/2时,函数f(x)=sinx+ cosx 【 】
已知△ABC的三个内角A,B,C满足A+C=2B, 1/cosA +1/cosC =/cosB ,求cos (A-C)/2的值.
(sin7°+cos15°sin8°)/(cos7° - sin15°sin8°)的值为________.
试证 (tana+tanb)/(tana-tanb)=sin(a+b)/sin(a-b).
证明 (sin²A-sin²B)/(sinAcosA-sinBcosB)=tan(A+B).
Prove that:(sin75°+sin15°)/(sin75°-sin15°)=tan60°
若A+B+C=180°,证:sin(B+2C)+sin(C+2A)+sin(A+2B)=4 sin1/2(B-C)∙sin1/2 (C-A)∙sin1/2(A-B)