x的两个平方根分别是3m-2和2m-8
则：3m-2+2m-8=0
5m=10
m=2
3m-2=4
2m-8=-4
所以：x=4²=16
x-y-2=3³
16-y-2=27
y=-13
5x+9y=80-117=-37