cos^4a/(cos^2b)+sin^4a/(sin^2a)=1 求证cos^4b/(cos^2a)+sin^4a/(sin^2b)=1

由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a sin b解题设a为锐角,证：1、2分之根3乘cos a + 2分之1乘sin a=cos(6分之π-a)2、cos a-sin a=根号2cos(4分之π+a) 化简cos(a+b)cos(a-b)+sin^2b sin^4+sin^2cos^2+cos^2a= 求证cos(a+b)cos(a－b)=cos^2b－sin^2a 求证cos(a+b)cos(a-b)=cos^2a-sin^2b 化简 sin^4a-cos^4b 化简sin^2acos^b-cos^2asin^2b+cos^a-cos^2b Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 cos^2a-cos^2b=m,那么sin(a+b)sin(a-b)=? 证明sin(A+B)sin(A-B)=cos^2B-cos^2A 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a=1.(不用向量怎么证?) 已知sin^4a/cos^2b+cos^4a/sin^2b=1,求证:sin^4 b/cos^2 a+cos^4b/sin^2a=1 已知(cos^4a)/cos^2b+(sin^4a)/sin^2b=1求证(cos^4b)/cos^2a+(sin^4b)/sin^2a=1 已知4sin asin b=根号2,4cos a cos b=根号6,则cos 2a+cos 2b的值是? sin(a-b)*cos a-cos(a-b)*sin a=1/5,则cos 2b的值是 cos^4a/(cos^2b)+sin^4a/(sin^2a)=1 求证cos^4b/(cos^2a)+sin^4a/(sin^2b)=1 cos(A+B)cos(A-B)化简的结果是（ ）A.cos^2A-sin^2BB.sin^2A-sin^2BC.cos^2A-cos^2BD.sin^2A-COS^2B怎么作的? 证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2B=1