[College Calculus] Integration by Partial Fractions Helps

So I'm supposed to integrate x/((x-1)(x^2 +1)), I've figured out that A = 1/2, and now I've grouped up like terms and factored out the variables to get to this point.

What I don't understand is how the equations in the brackets were made, why does a0 - a1 = 1 while the other equations are 0?

Thanks for the help!