x²+3ax+2a^2-a-1=0
x²+[(2a+1)+(a-1)]x+2a²-a-1=0
x²+(2a+1)x+(a-1)x+(2a+1)(a-1)=0
x[x+(2a+1)]+(a-1)[x+(2a+1)]=0
[x+(2a+1)][x+(a-1)]=0
x=-2a-1,x=-a+1