证1-tan2x/1+tan^2x=cos^2x-sin^2x

(cos^2 2x－sin^2 2x)/(1－tan2x)=(1+2sin2xcos2x)/(1+tan2x) 证明(1-2sin x cos x )/(cos^2x-sin^2x)=(1-tan x)/(1+tan x) 证明1-tan^2x/1+tan^2x=cos^2x-sin^2x 求证(tanxtan2x/tan2x-tanx)/(tan2x-tanx)+√3（sin^2x-cos^2x）=2sin 证(1/sin^2x)+(1/cos^2x)-(1/tan^2x)=2+tan^2x 已知tan=2,求(cos x+sin x)/(cos x-sin x)+sin^2x 设n>=2,当x不等于k派,求证：tanx*tan2x+tan2x*tan3x+.+tan(n-1)*tannx=tan 求证 （1—tan^2X)/(1+tan^2X)=cos^2X—sin^2X 求极限x趋于0时(1-cos(x/2))x / (tan x-sin x) 证明1/sin^x+1/cos^2x-1/tanx^2x=2+tan^2 已知tan2x=-2 π/2<2x<π求[2cos^2(x/2)-sinx-1]/根号2sin(π/4+x) 已知tan(x+y)=2/5,tan(x-y)=-1/4,则tan2x的值是