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已知0已知0已知00π/2cos(a+b)=-4/5,sina=3/5sin(a+b)=3/5cosa=4/5π/2所以sinb>0sinb=sin(a+b-a)=sin(a+b)cosa-sina*
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sin(a+b)=3/5
cosa=4/5
π/2
sinb=sin(a+b-a)
=sin(a+b)cosa-sina*cos(a+b)
=3/5*4/5-3/5*(-4/5)
=12/25+12/25
=24/25
cos(a+b)=cosa*cosb - sina*sinb = -4/5
sin(a+b)=sina*cosb + cosa*sinb = 3/5
sina = 3/5, cosa = 4/5
sinb = 24/25
0
则可求得：
sin(a+b)=-3/5或3/5，cosa=4/5
sinb=sin(a+b-a)
=sin(a+b)cosa-sina*cos(a+b)
=-3/5*4/5-3/5*(-4/5)
=0（因为π/2
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0
则可求得：
sin(a+b)=-3/5或3/5，cosa=4/5
sinb=sin(a+b-a)
=sin(a+b)cosa-sina*cos(a+b)
=-3/5*4/5-3/5*(-4/5)
=0（因为π/2
sinb=sin(a+b-a)
=sin(a+b)cosa-sina*cos(a+b)
=3/5*4/5-3/5*(-4/5)
=24/25
所以sinb=24/25
收起
你题目写错了吧
sina=3/5??
cos(a+b)=cosa*cosb - sina*sinb = -4/5
sin(a+b)=sina*cosb + cosa*sinb = 3/5
sina = 3/5, cosa = 4/5
sinb = 24/25