(cos a)^2 + (cos b)^2 =1
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
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
求证:a^2(cos^2b-cos^2c)+b^2(cos^c-cos^2a)+c^2(cos^2a-cos^2b)=0
已知cos(a+b)cos(a-b)=1/3 ,求(cosa)^2-(cosb)^2
cos(A+B)cos(A-B)=1/4 求cosA^2+cosB^2
cosacosb=1/2[cos(a+b)+cos(a-b)]如何证明
在三角形ABC中,cos^2A+cos^2B+cos^2C=1,则三角形的形状是?
化简(1-sin^6 a-cos^6 a)/(cos^2 a-cos^4 a)==
若cos(a+b)·cos(a-b)=1/3,则cos^2 a-sin^2 b的值是?
证明sin(4A)sin(2A)(1-cos(2A)) cos(4A)cos(2A)(1 cos(2A))=cos(2A
已知4sin asin b=根号2,4cos a cos b=根号6,则cos 2a+cos 2b的值是?