3sin^2a+2cos^2b=2sina 则sin^2a+cos^b的取值范围是我做了[0,1/2] 答案是[0,4/9]

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 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) 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 【(sin a+cos a)/(sin a-cos a) 】=3,tan (a-b)=2,tan (b-2a)=? sin^4+sin^2cos^2+cos^2a= 已知sin(a+b)sin(a-b)=-1/3,求cos^2a-cos^2b的值 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(a+b)cos(a-b)+sin(a+b)sin(a-b)=-3/5,求sin(3π/2+2b) 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a cos a+cosb=-1/3 sin a+sin b=1/2 求cos(a+b) sin(a-b)*cos a-cos(a-b)*sin a=1/5,则cos 2b的值是 已知sin[a-b]cos a-cos[b-a]sin a=3/5,b是第三象限角,求sin[b+5π/4]的值第一题1/2cos x-√3/2sin x第二题√3sin x+cos x第三题√2[sin x-cos x]第四题√2cos x-√6sin x 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急 化简cos(a+b)cos(a-b)+sin^2b 在三角形ABC 中,若sin A:sin B:sin C=3:2:4,则cos C的值