Completing the Square

Homeschooling Orla asked Dad for some help understanding what completing the square meant because the explanation in the text book was completely incomprehensible. In fact, Orla had made the mistake of referring to the textbook before watching a video on the matter. One quick video and it all made sense. But even after watching the video and understanding the concept, the textbook still didn't make sense. And since 'Dead Poets' Society' had recently been watched, an idea for a useful reference comment quickly emerged...