TeX source:

\begin{aligned} x^{2}-8 x-28 y-208 &=0 \\ x^{2}-8 x &=28 y+208 \\ x^{2}-8 x+16 &=28 y+208+16 \\ (x-4)^{2} &=28 y+224 \\ (x-4)^{2} &=28(y+8) \\ (x-4)^{2} &=4 \cdot 7 \cdot(y+8) \end{aligned}