感冒咳嗽能喝牛奶吗:已知:sin^2A/sin^2B+cos^2Acos^2C=1,求证:tan^2Acot^2B=sin^2C

已知:A,B,C为一个三角形的三个内角,证明:sin(A/2)+sin(B/2)+sin(C/2) <=2/3 已知向量M=(cos(A-B)/2,sin(A+B)/2) 已知sin^2A/sin^2B+cos^2Acos^2C=1,求证：tan^2Acot^2B=sin^2C 已知:sin^2A/sin^2B+cos^2Acos^2C=1,求证:tan^2Acot^2B=sin^2C sin(a+B)cosa-1/2{sin[(a+B)+a]-sinB}= 已知3sin^A+2sin^B=2sinA 求cos^A+cos^B的最值 已知锐角三角形ABC中,sin(A+B)=3/5,sin(A-B)=1/5,请问如何求证tanA=2tanB? 已知向量a=(cosα,sinα),b=(sinβ,cosβ),β属于(0，π),tanβ/2=1/2,向量ab=5/13．求sinβ,cosβ,sinα 已知：sinA+sin^2A=1 求sin^2+sin^4的值 三角形ABC 证明sin(A/2)*sin(B/2)*sin(C/2)<=1/8