cos(a-b)cos(a+b)+sin(a-b)sin(a+b)化简,

cos(a+b)+cos(a-b)/sin(a+b)+sin(a-b)化简 sin(a+B)cos(y-B)-cos(B+a)sin(B-y) 化简 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明 化简 sin^4a-cos^4b 化简[sin(2A+B)]/sinA-2cos(A+B) 化简：cos(A-B)cosB-sin(A-B)sinB cos(a-b)cos(b-c)+sin(a-b)sin(b-c)= sin（a-b）sin（b-r）-cos（a-b）cos（r-b) 貌似不难,sin（a+b）cos（c-b）-cos（b+a）sin（b-c）sin（a-b）sin（b-c）-cos（a 求证:cos(a+b)cos(a-b)=cos平方b-sin平方a 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a