化简cos^2B+cos^2(2/3Π-B) 答案是1-1/2sin(2B-Π/6)
1+sin2B/cos^2B-sin^2B=-3
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2
cos(a+B)×cos(a-B)=1/3,求cos^2(a)-sin^2(B)的值
1、cos(x+B)*cos(x-B)=cosx-sin^2B
若cos(a+b)·cos(a-b)=1/3,则cos^2 a-sin^2 b的值是?
化简sin^2(a)*sin^2(b)+cos^2(a)*cos^2(b)-1/2cos2a*cos2b
cos(A-B/2)=-1/9,sin(A/2-B)=2/3,A是第二象限角,B是第一象限角,cos(A+B)=?
已知cos(a+b)=0,求值:sin(π+2a+b)-cos(-π/2+2a+3b)
设cos(a-b/2)=-1/9,sin(a/2-b)=2/3,其中a属于(π/2,π),b属于(0,π/2),求cos
已知0<A<π/2<B<π,cos(B-π/4)=1/3,sin(A+B)=4/5求cos(a+
已知三角形ABC是锐角三角形,且sin(B-6分之π)cos(B-3分之π)=2分之1 求角B的