Problem: The graph above shows the function g, where g(x) = k(x+3)(x-3) for some constant k. If g(a-1.2)=0 and a>0, what is the value of a?
If you plug a-1.2 in for x, you get $\displaystyle g(a-1.2) = k((a-1.2)+3)((a-1.2)-3) = k(a+1.8)(a-4.2)=0$. So either $\displaystyle a+1.8=0$ or $\displaystyle a-4.2=0$; however, a>0...so which answer will it be?