cos (2x-π/3)=2sinπ/4

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 (2x-π/3)=2sinπ/4 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- 证明sin^2(x)+cos^2(x+30)+sin(x)cos(x+30)=3/4 求证:(sin 2x /(1-cos 2x) )·(sin x /(1+sin x))=tan (π/4-x/2). 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 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 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 求函数y=cos(9/2π+x)+sin^2x的最大值和最小值还有一题 已知sinx+cosx=1/2,求sin^3x+cos^3x和sin^4x+cos^2x f(x)=cos(2x-x/3)+2sin(x-π/4)sin(x+π/4)sin(x+π/4)化简. y=2cos(x/4+ π/3)-3sin(x- π/4)y=sin(4x- π/3)-cos(3x+π/2) 已tanx=4/3,求cos(2x-π/3)cos(π/3-x)-sin(2x-π/3)sin(π/3-x) 已知sinx+cosx/sinx-cosx=2,求2cos(π-x)-3sin(π+x)/4cos(-x)+sin(2π-x) 函数fx=cos(2x-π/3)+2sin(x-π/4)sin(x+π/4)怎么化简? 已知sin(x+π/3)=1/4,求sin(2π/3-x)+cos²(π/6-x) 为什么cos(2x-π/3)-sin(5π/6) =cos(2x-π/3)?