∵(a+1)²+/b-3/=0
∴a+1=0
b-3=0
∴a=-1
b=3
(a+2b)²-(2a+b)(a-b)-2(a-b)(a+b)
=a²+4ab+4b²-(2a²-ab-b²)-2(a²-b²)
=a²+4ab+4b²-2a²+ab+b²-2a²+2b²
=-3a²+5ab+7b²
=-3-15+7
=-11