f(x)=x^2-15x
What are the zeros of the quadratic function?
\left \begin{array}{rcl} x^2-15x&=&0\\ x(x-15) &=&0 \end{array} \right\} \quad x_1=0\qquad (x_2-15) = 0 \quad \Rightarrow \; x_2=15
