当a=3pai /4时,sin (a+b)+cos (a+b )+sin (a-b)+cos (a-b)等于:A 1 B
cos(a+b)=3/5 sin(b-pai/4)=5/13 a,b 属于(0,pai/2) 求cos(a+pai/4)
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
若cos(A+B)cos(A-B)=1/3 则cos平方A-sin平方B 等于
已知tan(a+b)=2/5,tan(b-pai/4)=1/4,求(cos a+sin a)/(cos a-sin a)
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
cos(a-b)=12/13,sin(a+b)=-3/5,求cos(pai/2-2a)
cos(a+b)+cos(a-b)/sin(a+b)+sin(a-b)化简
cos(a-b)cos(b-c)+sin(a-b)sin(b-c)=
sin平方a*cos平方b-cos平方a*sin平方b为什么等于sin平方a-sin平方b?
求证:cos(a+b)cos(a-b)=cos平方b-sin平方a
cos(a+B)×cos(a-B)=1/3,求cos^2(a)-sin^2(B)的值