cos(π/4+x)=3/5,则sin(π/4-x)=?

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 cos(π/4+x)=3/5,则sin(π/4-x)=? tanx=m,则{sin(x+3π）+cos(π+x)}/{sin(-x)-cos(π+x）}=? 2sin^2x - 5sin x cos x=3 cos^2x,求X, 已知sinα+cosα=4/5且3π/22,若sinα+sinβ+sinγ=0,cosα+cosβ+cosγ=0,则cos(α-β)的值 cos(π/6-x)=根号3/3则cos(5π/6+x)-sin(x-π/6)的平方 已知 sinα + cosα / sinα - cosα = 2 ,则 sin(α-5π) x sin(3π/2-α)等于A,3/4B,±3/10C,3/10D,-3/10 已知cos 2x=3/5,求sin^4 x+cos^4 x的值 化简sin(3π-x)cos(x-3/2)cos(4π-x)/tan(x-5π)cos(π/2+x)sin(x-5/2π) 化简sin(3π-x)cos(x-3/2)cos(4π-x)/tan(x-5π)cos(π/2+x)sin(x-5/2π) 若cos x-sin x = 0.5,则cos^3 x-sin^3 x = 证明sin^2(x)+cos^2(x+30)+sin(x)cos(x+30)=3/4 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！】 若sin(π/2+x)=-4/5,x属于（π/2,π）,则cos(π/3-x)= cos (2x-π/3)=2sinπ/4 为什么cos(2x-π/3)-sin(5π/6) =cos(2x-π/3)? 高数三道大题求解析17.化简sin(2π-α)cos(π/2+α)cos(π/2-α)/[sin(3π-α)sin(-π-α)sin(π/2+α)]=多少?18.若cos(α+π/3)=4/5,α∈（0,π/2）,则cosα=多少?19.已知函数f(x)=1+√2cos(2x-π/4)/[sin(x+π/2)](1)求f（x）的定义 已知sin（x+π÷6）=1/4,则sin（5π/6-x）+cos^2（π/3-x）=