Bài 4: Thực hiện phép tính (quy đồng) 1) \(\frac{2}{x+3} + \frac{x}{3-x} - \frac{x^2}{x^2-9}\) 2) \(\frac{1}{x-2} + \frac{1}{x+2} - \frac{4x-4}{x^2-4}\) 3) \(\frac{2}{x-2} + \frac{3}{x+2} - \frac{18-5x}{x^2-4}\) 4) \(\frac{x+1}{x+3} - \frac{x-1}{3-x} + \frac{2x-2x^2}{x^2-9}\) 5) \(\frac{4}{x+2} + \frac{3}{2-x} + \frac{12}{x^2-4}\) 6) \(\frac{4}{x+2} + \frac{2}{x-2} - \frac{5x-6}{4-x^2}\) 7) \(\frac{x^2}{x^2-4} + \frac{1}{x+2} + \frac{2}{2-x}\) 8) \(\frac{a^2}{a+1} + \frac{1}{a-1} - \frac{2a}{a^2-1}\) 9) \(\frac{1}{x+2} + \frac{2}{x-2} + \frac{x}{x^2-4}\) 10) \(\frac{x+1}{x-3} - \frac{1-x}{x+3} - \frac{2x(1-x)}{9-x^2}\) 11) \(\frac{1}{x-y} + \frac{2}{x+y} + \frac{3x}{y^2-x^2}\) 12) \(\frac{x}{x+y} + \frac{y}{x-y} + \frac{2xy}{y^2-x^2}\)