13. Incorrect. The answer is false, not true. d/dx[f(x)/g(x)] = [f'(x)*g(x)- f(x)*g'(x)]/[g(x)]². d/dx[(5x²-3x)/(x² + 1)] =[(10x -3)(x² + 1) - 2x (5x² - 3x)]/(x² + 1)² = (-3x² + 10x - 3)/ (x² + 1)²