证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y)

证明tan(90°-y)=(2cos^3y-cosy)/(siny-2sin^3y) 证明tan(x+y)+tan(x-y)=sin2x/cos^2x-sin^2y 证明：(1) sin(360°-α)=-sinα(2)cos(360°-α)=cosα(3)tan(360°-α）=tanα 请问怎么证明sinX+sin(X+Y)+sin(X+2Y)/cosX+cos(X+Y)+cos(X+2Y)=tan(X+Y), 证明sinx+cos(x+y)siny/cosx-sin(x+y)siny=tan(x+y) 高中三角函数证明y=-t^2/2 + 1/2设t=tanθ及y=[(cos^2θ-sin^2θ)/2sinθcosθ ] * tanθ证明y=-t^2/2 + 1/2 证明tanα/2=1-cosɑ/sinɑ 证明tan a/2=sin a/(1+cos a) 求证cos（720°+α）（2/cosα+tanα）（1/cosα-2tanα）=2cosα-3tanα 证明（3－4cos 2A＋cos 4A） / （3＋4cos 2A＋cos 4A）=tan^4 A 证明[2-2sin(α+3π/4)cos(α+π/4)]/(cos^4α-sin^4α)=(1+tanα)/(1-tanα) 证明下列各题：(1)cos20°(tan40°-根号3)=-tan40°；(2)sin(α+β)-2cosαsinβ=tan(α-β)[2cosαcosβ-cos(α+β)]. tan(x+y)=7,tanx*tany=2/3,则cos（x-y）=? cos(2x+y)=3cosy,求tanx*tan(x+y) 证明:1-2sinα cosα/cos^2α -sin^2α=1-tanα/1+tanα 5cos(x-y/2)+7cos(y/2)=0求tan(x/2)*tan[(x-y)/2] 证明:cos^4 a-sin^4 a=cos^2 a(1-tan a)(1+ tan a) 证明1/cos^α-tan^2α-sin^2α=cos^2α