sin(x- 3π/4)cos（x- π/4）=—1/4 求cos4x

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) 化简2sin^2[(π/4)+x]+根号3（sin^x-cos^x）-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 化简sin(x+7π/4)+cos(x-3π/4）步骤我已经找到撒sin(x+7π/4)+cos(x-3π/4)=sin(x+2π-π/4)+cos(x-π+π/4)我问下这一步是在干嘛?=sin(x-π/4)+cos[-(π-x-π/4)]=sin(x-π/4)+cos(π-x-π/4)=sin(x-π/4)-cos(x+π/4)=sin(x-π/4)-cos(x+π/2- cos (2x-π/3)=2sinπ/4 f(x)=2sin^2(π/4+x)+根号3(sin^2x+cos^2x)f(x)=2sin^2(π/4+x)+根号3(sin^2x-cos^2x) 符号打错了 f(x)=cos(2x-x/3)+2sin(x-π/4)sin(x+π/4)sin(x+π/4)化简. 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 f(x)sin^4x+cos^4x-1/sin(3π/2+x)cos(3π/2-x)的奇偶性 sin（π/4-x)为什么等于cos(x+π/4) 化简sin(x-π/4)+cos(x+π/4) cos(x+π/4)+sin(x+π/4)化简 cos(x+π/3)是不是等于sin(x-π/6) cos(π/6-x)=sin(π/3+x)?为什么 求证:(sin 2x /(1-cos 2x) )·(sin x /(1+sin x))=tan (π/4-x/2). tanx=m,则{sin(x+3π）+cos(π+x)}/{sin(-x)-cos(π+x）}=? 函数y=sin(x)cos(x+ π/4)+cos(x)sin(x+π/4)的最小正周期是