若cos(π/2+x)=4/5,则cos2x=

5cos^2a+4cos^2β=4cosα则cos^2a+cos^2β 若x=π/12,则cos(2x-π)*cos[2(x-π)]=? 若sinx+sin^2x=1,则cos^2x+cos^4x=? 若cos (x+30°)+sin x =4/5,则cos (2x-60°)等于? cos(2x-π)/[根号2cos(x+π/4)]=-1/5,0 若cos(x+y)=4/5,cos(x-y)=-4/5,且3π/2 若sinx=4/5,cos（x-β）=-3/5且x∈（0.π/2）,β∈（-π/2.0）,则cosβ等于 若cosx=2/3,x是第四象限角,求sin(x-2π)+sin(-x-3π)cos(x-3π)/cos(π-x)-cos(-π-x)cos(x-4π)的值 三角函数解方程 (cos 3x)^3+ (cos 5x)^3 = 8 (cos 4x)^3 (cos x)^3 计算：cos（π/5)+cos（2π/5)+cos(3π/5)+cos(4π/5) 一道算术题目↓↓x^2=5-4cosαx^2=25-24cosβcosα+cosβ=0 求X值 若2cos(3π-x)=cos(π/2+x),则sin(π+2x)= 若F(sin x)=3-cos 2x 则F（cos x）=? 若sinx+sin^2x=1,则cos^2x+cos^4x=?由 sinx+sin^2x=1得 sinx=1-sin^2x=cos^2xcos^2x+cos^4x=cos^2x(1+cos^2x)=sinx(1+sinx)=sinx+sin^2x=1cos^2x(1+cos^2x)=sinx(1+sinx)怎么来的? 已知cos 2x=3/5,求sin^4 x+cos^4 x的值 f(cos)=-cos(2x),则f(sinx) 求值:cos(π/11)cos(2π/11)cos(3π/11)cos(4π/11)cos(5π/11) 求值：cos(π/11)-cos(2π/11)+cos(3π/11)-cos(4π/11)+cos(5π/11)