x为锐角
cos x=5/13 ,sinx=12/13
tanx=12/5
tan(x+y)
= (tanx+tany)/(1-tanx*tany)=-120/119
119*(12/5+tany)=120*12/5*tany-120
解得:tany=12/5
x及y为锐角,又tanx=tany
所以,x=y