\[(x - 2)^{2} - (x - 1)(x + 2) =\]
\[= x^{2} - 4x + 4 - \left( x^{2} + 2x - x - 2 \right) =\]
\[= x² - 4x + 4 - x^{2} - x + 2 = - 5x + 6\]