90°
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90°90°90°由题意,sin(x-y)=5/13cos(x+y)=-4/5∴sin2x=sin[(x+y)+(x-y)]=sin(x+y)cos(x-y)+sin(x-y)cos(x+y)=-36
90°
90°
90°
由题意,
sin(x-y)=5/13
cos(x+y)=-4/5
∴sin2x
=sin[(x+y)+(x-y)]
=sin(x+y)cos(x-y)+sin(x-y)cos(x+y)
=-36/65-20/65
=-56/65
cos(2x)=-33/65