sin(a)*cos(a)=4,那么sin(a) cos(b)=?
sin(a)*cos(a)=4,那么sin(a) cos(b)=?
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
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
已知tan a=cos a,那么sin a=
cos(a-b)cos(b-c)+sin(a-b)sin(b-c)=
求证:cos(a+b)cos(a-b)=cos平方b-sin平方a
cos^B-cos^C=sin^A,三角形的形状
sin²A+sin²B=cos²C
证明cos(a+b)=cos(a)cos(b)-sin(a)sin(b)详细步骤,书上的证明看不懂.
(1-sin^6a-cos^6a)/(1-sin^4a-cos^4a)=?
Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2