sin^2a=sin^2a/sin^2a+cos^2a=tan^2a/tan^2a+1为什么

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)=2sin(b)求sin(a/2)/sin(b/2)的值. 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 若sin^2a sin^2(-a)化简 3 在三角形ABC中,已知（a2+b2）sin（A-B）=（a2-b2）sin(A+B) 求证：ABC是等腰或直角三角形(a^2+b^2)sin(A-B)=(a^2-b^2)sin(A+B),(sin^A+sin^B)sin(A-B)=(sin^A-sin^B)sin(A+B) sin^A*(sin(A+B)-sin(A-B))=sin^B*(sin(A-B)+sin(A+B)) sin^A*2c (cos a)^4+(sin a)^2*(sin a)^2+(sin a)^2=? cosA+cos^2A=1,sin^2A+sin^4A+sin^8A 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^2(丌+a)= 证明sina sin(a+2b) - sinb sin(b+2a) =sin(a+b)sin(a-b) sin a+sin 2a +sin 3a +...+sin na怎么求和? sin a+sin 2a +sin 3a +...+sin na怎么求和?