斜率为1
x-y+a=0
(x-3)²+(y+2)²=13
圆心(3,-2),半径√13
圆心到切线距离等于半径
|3+2+a|/√(1²+1²)=√13
|a+5|=√26
a=-5±√26
x-y-5+√26=0和x-y-5-√26=0