a/(a+3) = (2a)/(a - 3) - 1
if you want to find values of a where this is true, then putting all over a common denominator of (a+3)(a-3), we have
-9(a+1) / (a^2-9) = 0
so, a = -1
a graph can be seen at
http://www.wolframalpha.com/input/?i=solve+a%2F%28a%2B3%29+%3D+%282a%29%2F%28a+-+3%29+-+1