rearrangement mechanical puzzles : Here the pieces have to be rearranged in a certain way in order to achieve a certain setup. Sometimes such the puzzles is presented in a solved state, but is easily changed into a difficult setup by a few moves by the player.
... getting
<math>x^2+\frac{b}{a}x+\frac{b^2}{4a^2}=-\frac{c}{a}+\frac{b^2}{4a^2}.</math>
The left side is now a perfect square; it is the square of (x + ...