(sin^2b+cos^2b)^2-2sin^2bcos^2b=1-1/2sin^2b这里的1/2sin^22b是怎么得来的

化简cos(a+b)cos(a-b)+sin^2b 化简sin^2a+sin^2b-sin^2a*sin^2b+cos^2a*cos^2b sin^2a+sin^2b-sin^2a * sin^2b+cos^2a * cos^2b 化简 sin^2 (A)+sin^2(B)-sin^2(A)sin^2(B)+cos^2(A)cos^2(B) 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 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 化简sin^2acos^b-cos^2asin^2b+cos^a-cos^2b 求证cos(a+b)cos(a－b)=cos^2b－sin^2a 求证cos(a+b)cos(a-b)=cos^2a-sin^2b sin(a-b)*cos a-cos(a-b)*sin a=1/5,则cos 2b的值是 化简（sin(a-b)-2sin a cos b）/2sin a sin b +coa(a+b) Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 化简[sin(2A+B)]/sinA-2cos(A+B) sin(2a-b)-2cos(a+b)sina/sinb 求sin^2B+cos^2B=?如题 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