## Algebra: A Combined Approach (4th Edition)

We will add $\frac{25}{4}$ to make $x^2-5x$ a perfect square trinomial.
We add the square of half of the coefficent of $x$ so that the result is a perfect square trinomial. Co-efficient of $x=-5$ Half of -5 is $\frac{1}{2}×-5=\frac{-5}{2}$ Square of $\frac{-5}{2}$ is $\frac{-5}{2}×\frac{-5}{2}=\frac{25}{4}$ We add $\frac{25}{4}$ to $x^2-5x$ to make it a perfect square trinomial.