4*sin^2b+4/9cos^2b=1 我求出来的COS^2b=27/32 b是个角

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) 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 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?) cos^4a/(cos^2b)+sin^4a/(sin^2a)=1 求证cos^4b/(cos^2a)+sin^4a/(sin^2b)=1 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 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 cos(B/2)sin(B/2)=1/4,求角B 4*sin^2b+4/9cos^2b=1 我求出来的COS^2b=27/32 b是个角 sin(a-b)*cos a-cos(a-b)*sin a=1/5,则cos 2b的值是 Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 若log2/1(sin a)+log2/1(sin b)=2,(27^cos a)^cos b=1/9,cos(2a+2b)=? 1-1/4sin^2 2A-sin^2B-cos^4Asin(A+B)=3/5sin(A-B)=-4/5 设sinα+sinβ=1/3,则sinα-cos方β的最大值是A 4/3 B 4/9 C -11/12 D -2/3cos方β=cos的平方β 4.19-4/ 已知cos[a-(b/2)]=-1/9,sin[(a/2)-b]=2/3,∏/2 证明cosA＋cosB＋cosC=1+4sin(A/2)sin(B/2)sin(C/2)证明：cosA＋cosB＋cosC=1+4sin(A/2)sin(B/2)sin(C/2)尽量详细一点选做cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) cos(180-B-C)+cosB+cosC=1+2sin(A/2)[2sin(B/2)sin(C/2)] cos(180-B-C)+cosB+cosC 证明 三角函数 不等式用恒等式2cosAsinB=sin(A+B)-sin(A-B)证明：2[cosβ+cos(β+2α)+cos(β+4α)]sinα=sin(β+5α)-sin(β-α).推导出：cosβ+cos(β+2π/3)+cos(β+4π/3)=0.解不等式：√(x+5)≤1+|x|.【一共有两题啊！】 已知4sin asin b=根号2,4cos a cos b=根号6,则cos 2a+cos 2b的值是?