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ǰλãҳ>>cos(-a)=cos aΪʲô>>

cos(-a)=cos aΪʲô

cos(a-) =cos(-a) =-cosa (2ޣcosa

һ: cos(a-b)=cosacob+sinasinb cos(b-a)=cosacob+sinasinb sin(a-b)=sinacosb-sinbcosa sin(b-a)=sinbcosa-sinacosb tan(a-b)=(tana-tanb)/(1+tanatanb) tan(b-a)=(tanb-tana)/(1+tanatanb) cos(a-b)=cos(b-a) sin(a-b)=-sin(b-a) tan(a-b)...

Ǻʽ: cos(-a)=cos a cos(aC90)=cos-[(90-a)]=cos(90Ca)

ż䣬ſޡ-cosa cos(--a) =cos[-(+a)] =cos(+a) = -cosa

cos(a-b)=cosacosb+sinasinbǺȱ任Ĺʽ ɣлл

cos-a+c =cos[/2-(a-c-/2] =sina-c-/2 =-sin/2-a+c =-cosa-c

Ϊ A+B+C=180 cosC=cos(180-(A+B))=-cos(A+B) sinC=sin(180-(A+B))=sin(A+B) õյʽ cos180-a=-cosa sin180-a=sina

cos(90+a)-sina ż䣬ſޡ յ90㣬䣻90+ܦʹյʽʱҪǣ90+Ҫڶ޵Ľǣڶ޽ǵֵǸģcos(90+a)-sina. ǸǴģ

ȽֱϵֱϵxOyλԲOa,b-bʹaĿΪOxԲOڵP1ձ߽ԲOڵP2bʼΪOP2ձ߽ԲOڵP3-bʼΪOP1ձ߽ԲOڵP4ʱP1P2P3P4ֱΪ  P110...

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