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ΪʲôCos(-x)=Cosx

ȻλԲ cosֵļ

Ϊy=cosxż cos(-x)cosx

Ϊڵ1͵4cosǵķŶһġ

-sinx

cosxż

Ϊcos(360-x)=cosx ԣ cos(180+x)=cos[360-(180+x)]=cos(180-x) Ƕ-cosx

Ϊ180= ߦ-xڵڶ,Ϊ,cos(-x=-cosx עcosxڵһΪ,ڶΪ.

cos(x+y)-cosx=0 2SIN(x/2)SIN(x+y/2)=0 SIN(x/2)=0SIN(x+y/2)=0 x/2=kлx+y/2=k x=2kлy=2k-2x kΪ

ݱ᲻䣬ſޡ90ӣsinΪcos,xǣ90+xΪ۽ǣsin(90+x)Ϊ,cosx.ͨõķ

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