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ǰλãҳ >> ΪʲôCos2x=1%2(sinx)^2 >>

ΪʲôCos2x=1%2(sinx)^2

cos2x=(cosx)^2-(sinx)^2 =1-(sinx)^2-(sinx)^2 =1-2(sinx)^2

⣺ cos2x=cos(x+x) =cosx*cosx-sinx*sinx =(cosx)^2-(sinx)^2 ʽӦõcos(x+y)=cosx*cosy-sinx*sinyx=y

cos(x+y)=cosxcosy-sinxsiny Ȼ Ƶ cos2x=cos(x+x) cos(x+x)=cosxcosx-sinxsinx=(cosx)^2-(sinx)^2 ϣﵽ㡣 ֻǸһѧд©ָ̡

cos2x=cos^2x-sin^2x=1-2sin^2x=2cos^2x-1 μ

cos2x=cos(x+x) cosx^2-sinx^2=cos2x +1 cosx^2+1-sinx^2=cos2x 2cosx^2=1+cos2x cosx^2=(1+cos2x)/2

ʽx=Pi/6sin(x)^4=1/16Ҷ=3/8.֪ⲻһʽ

ʵe^x1ȼxln(1+x)ȼxsinxȼx1(1+sinx)^x1e^(xln(1+sinx))1ȼxln(1+sinx)ȼxsinxȼx^22ش﷨(tanx)^xlim(tanx)^x=e^(limxlntanx)=e^(limlntanx/(1/x))e^(limsec^2x/tanx/(...

## ̩չʽ ˼·ȫȷӦsinx̩չˣοͼ

cos2x=1-2sin^x=1-2x^2 sinx/2=x/2 lim[x->0](1+x/2-2x^2)^[(2/x)*1/2]=e^0.5

Ϊ 1-cosx~x^2/2 xȫ2xǵȼ۵ģ 1-cos2x~2x)^2/2=4x²/2

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