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ǰλãҳ >> Ϊʲôsin2x=2sinxCosx >>

Ϊʲôsin2x=2sinxCosx

sin2x =sin(x+x) =sinxcosx+cosxsinx =2sinxcosx

ϸдֽ

ԴӺͽǹʽôƵ sin2x=sin(x+x) =sinxcosx+cosxsinx =2sinxcosx

sin2x=2sinxcosx sin4x=2sin2xcos2x Ը⣬ԼΪxǺ עⱶǹʽеĽǵıԵģ42211/2Ķ

¥ sinAcosA+cosAsinA = sinAcosA+sinAcosA Ȼ󲻾2sinAcosA

⣺fcosx=2-sin2x=2-2sinxcosxcosx=tsint=̣1-t^2ft=2-2ṭ1-t^2t=sinxfsinx=2-2sinxcosxfsinx=2-sin2x

⣺ fcosx=2-sin2x=2-2sinxcosx cosx=t sint=̣1-t^2 ft=2-2ṭ1-t^2 t=sinx fsinx=2-2sinxcosx fsinx=2-sin2x

ԴƣԵõǹʽ.....

lim[(sin2x)/x]=lim[(2sinxcosx)/x]=lim{[(2sinx)/x]•cosx}

֪ʽ sin(a+b)=sinacosb+cosasinb a=b룬͵õҪĹʽ

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