cos²a-cos²b=c,则sin(a+b)sin(a-b)=
sin²A+sin²B=cos²C
cos(a-b)cos(b-c)+sin(a-b)sin(b-c)=
sin²(a+b)+cos²(a+b)=
cos^B-cos^C=sin^A,三角形的形状
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
在三角形中,已知,cos C/cos B=(3a-c)/b 求:sin B
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
求证:cos(a+b)cos(a-b)=cos平方b-sin平方a
貌似不难,sin(a+b)cos(c-b)-cos(b+a)sin(b-c)sin(a-b)sin(b-c)-cos(a
sin(A+B/2)=cos(C/2)
若sin/a=cos/b=cos/c,则三角形是?