求证sin^4a+cos^4a=1
求证sin^4a+cos^4a=1-2sin²acos²a
求证:sin a (1+cos2a)=sin a cos a
求证sin^4a-cos^4a=-cos2a
求证:tan a/2=(1-cos)/sin a=sin a/(cos a+1)
求证sin(90+a)=cos a
(1-sin^6a-cos^6a)/(1-sin^4a-cos^4a)=?
求证:sin a(1+tan a)+cos a(1+1/tan a)=1/sin a+1/cos a
化简(1-sin^6 a-cos^6 a)/(cos^2 a-cos^4 a)==
证明sin(4A)sin(2A)(1-cos(2A)) cos(4A)cos(2A)(1 cos(2A))=cos(2A
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
求证sin 4次方a+cos 平方a+sin 平方acos 平方a=1
求证 2(1-sin a)(1+cos a)=(1-sin a + cos a)^2