若sin^2 40度+sin^2 a=1,且a为锐角,则a=?

1-sin a+sin a的平方-sin a的立方+……若a是正锐角,且sin a-cos a=0.5,求1-sin a+sin^2a-sin^3a+…… 若sin^2 40度+sin^2 a=1,且a为锐角,则a=? 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a 懂得进.证明,sina+sin(a+b)+sin(a+2b)+...sin(a+nb)=sin(a+ab/2)sin[(n+1)b/2]/sin(b/2) 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 【证明】Sin A+sin B=2Sin 22 cosA+cos^2A=1,sin^2A+sin^4A+sin^8A sin(arccos(2sin(a)))= 在△ABC中,求证；sin^(A/2)+sin^(B/2)+sin^(C/2)=1-2sin(A/2)sin(B/2)sin(C/2） 证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2B=1 若sin^2a sin阝=1/3,sin(a+阝)=1,求sin(2a+3阝) 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 Rt三角形中 角c等于九十度 求证 sin^2A?tanA+sin^2B?tanB=1-2sin^2A?sin^2B/cosA?cosB 已知sin(a)=2sin(b)求sin(a/2)/sin(b/2)的值. 若a为锐角,sin^2(48°)+sin^2(a)=1