a²+b²=2a-8b-17
a²+b²-2a+8b+17=0
(a-1)²+(b+4)²=0
a-1=0,b+4=0
a=1,b=-4
(b/2)^2a+b^(-a)
=(-2)^2+(-4)^(-1)
=4-1/4
=15/4