Tìm x a) (3x - 1)² - 5(2x + 1)² + 3(2x + 1)(x - 1) = (x - 1)² b) \(\frac{1}{2}(x - 5) - \frac{1}{4}(x - x) = \frac{1}{5}(x + 1) - \frac{1}{10}(3 + x)\)