-π/2<Y<0,sinY=-5/13,则cosY=12/13
(a-b)2=a2+b2-2ab=2-2cos(X+Y)
(a-b)2=4/5
cos(X+Y)=3/5
sin(X+Y)=-4/5或4/5
sinX=sin(X+Y-Y)
=sin(X+Y)cosY-cos(X+Y)sinY
=63/65或-33/65(舍去),
因为0<X<π/2,sinX>0
-π/2<Y<0,sinY=-5/13,则cosY=12/13
(a-b)2=a2+b2-2ab=2-2cos(X+Y)
(a-b)2=4/5
cos(X+Y)=3/5
sin(X+Y)=-4/5或4/5
sinX=sin(X+Y-Y)
=sin(X+Y)cosY-cos(X+Y)sinY
=63/65或-33/65(舍去),
因为0<X<π/2,sinX>0