This is a part of a kinetic equation of motion,
\begin{align} x(t) - x_0 &= \frac{1}{2}a \left[ \frac{v(t) - v_0}{a} \right]^2 + v_0 \left[ \frac{v(t) - v_0}{a} \right] \tag{1.17} \\ &= \frac{v(t)^2 - v_0^2}{2a} \, . \tag{1.18} \end{align}
I am interested in how one passes from 1.17 to 1.18. I am not sure if this is the proper format for a question.