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ΪʲôCos(-x)=Cosx

ȻλԲ cosֵļ

һλ԰ ǣһxһ-x Կcosx=OA/R //: ҺĶ cos(-x)=OA/R ˣ cos(-x) = cosx ͼ

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

Ϊy=cosxż cos(-x)cosx

Ǻʾģ cosxż ԣcos(-x)=cosx ԣy=1-cos(-x)=1-cosx

Ͳʽ Уa=x+hb=x

1ݹʽcos(A+B)=cosA*cosB-sinA*sinB, A=B=Xɵùʽ 2ԭʼ֪ʶʼƵ ȽֱϵֱϵxOyλԲOa,b-bʹaĿΪOxԲOڵP1ձ߽ԲOڵP2bʼΪOP2ձ߽ԲO...

ô

Ϊcos(x+h)-cosx=-2sin(x+h/2)sin(h/2) :lim [cos(x+h)-cosx]/h =lim[-2sin(x+h/2)sin(h/2)/h] =lim[-sin(x+h/2)sin(h/2)/(h/2)] =lim[-sin(x+h/2)] =-sinx

arccos֪cos=x arccosx=֮cos=cos(arccosx)=x 😊😊😊😊😊😊😊😊😊😊😊

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