sin a =2乘以sin (90-a) 求a的度数

sin a =2乘以sin (90-a) 求a的度数 sin(80+2a)/1+cos2a乘以cos^2a/cos(90+a)= 证明 sin^4a+cos^4a=1-2sin^2a乘以cos^2a 已知sin(π+a)=1/2,求sin(2π-a)-1/tan(a-π)乘以cosa的值.已知sin(π+a)= 1/2,求 {sin(2π-a)-1}/{tan(a-π)} 乘以{cosa}的值 sin(arccos(2sin(a)))= 【证明】Sin A+sin B=2Sin 22 证明sin(a+b)sin(a-b)=sin^2 a-sin^2 b, 求证:sin(a+b)sin(a-b)=sin^2a-sin^2b 已知：sin(a+b)=1/2 ,sin(a-b)= 1/3 ,则 tana 乘以 cotb 等于多少. 设A,B为锐角,且sin^2A+sin^B=sin(A+B),求证A+B＝90sin^2A+sin^2B=sin(A+B)sin^2A表示sinA的平方 sin^2a乘以tana+cos^2a乘以cota+2sina乘以cosa-cota 已知sin(a)=2sin(b)求sin(a/2)/sin(b/2)的值. cos平方a-cos平方b=A -cos｛a+b｝乘以cos｛a-b｝Bcos｛a+b｝乘以cos｛a-b｝C-sin｛a+b｝乘以sin｛a-b｝Dsin｛a+b｝乘以sin｛a-b｝要过程 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a sin 2a+2sin方a/ 1+tan a =2sin a cos a 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急 sinA-sinB=2倍的sin【(A-B)/2】乘以cos【(A+B)/2】?为什么? 求证：sin²a+sin²β-sin²a×sin²β+cos²a×cos²β=1x是乘以