la-b+3l+(2a+b)^2=0
a-b+3=0
2a+b=0
解方程组得：
a=-1,b=2
2a^3b(2ab+1)-a^2(-2ab)^2
=4a^4b^2+2a^3b-4a^4b^2
=2a^3b
=2*(-1)^3*2
=-4