题目应是 a²+6a+b²-b+37/4=0
a²+6a+9+b²-b+1/4=0
(a+3)²+(b-1/2)²=0
a+3=0 b-1/2=0
a=-3 b=1/2
代数式a²-2b的值
=(-3)²-2*1/2
=9-1
=8