若实数x,y满足圆的方程 求x-y的取值范围

直线x-y-C=0要与圆有交点
则(3,4)到直线的距离<=2
=>
|3-4-C|/√2 <=2
=>
-1-√2<=C<=-1+2√2

设x=3+2*cosa ,y=4+2*sina
x-y=2(cosa-sina)-1=2（根号2）*[cos(a+45°)]-1
-2(根号2)-1《x-y《2（根号2）-1.