证明 sin(A+B)cos(A-B)=sinAcosA+sinBcosB

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sin(a+b)cos(a-b)
=(sinacosb+cosasinb)(cosacosb+sinasinb)
=sinacosa(cosb)^2+(cosa)^2sinbcosb+(sina)^2sinbcosb+sinacosa(sinb)^2
=sinacosa(cosb)^2+sinacosa(sinb)^2+(cosa)^2sinbcosb+(sina)^2sinbcosb
=sinacosa+sinbcos

数学证明恒等式sin(a+b)cos(a-b)=sinacosa+sinbcosb cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明证明cos(a+b)=cos(a)cos(b)-sin(a)sin(b)详细步骤,书上的证明看不懂. sinAcosA=sinBcosB sin2A/2=sin2B/2 得2A=2B或 2A+2B=180 ° ,2A+2B 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a 证明三角函数等式sin(A+B)-sinA=2cos(A+B/2)sin(B/2) 证sin^2a x tana+cos^2a x cota+2sinacosa=1/sinacosa 证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a 和差倍半公式怎么证明怎么用单位圆证明sin（a ± b）=sin a x cos b ± cos a sin bcos（ [三角函数]1,已知2sin^2a+3sinacosa-2cos^2a=0,则tana为?2,三角形两内角为A、B,且点 sinb/sina=cos(a+b),证明3sinb=sin(2a+b)