<p>auburn math tutor, did you take calc 2? 9.999… can be represented as 9/1+9/10+9/100+… or more concisely as sigma(9/(10^n),0,inf) is a geometric series, the formula for the convergence of which is a/(1-r) where a=9 and r=1/10, so 9/(1-1/10)=9/(9/10)=10. therefore 10=9.999… if you want exactly the OP subtract off 9 from each side, but you get the idea, everyone learns how to do this equation freshman year, though most don’t realize it.</p>