Question:medium

Find: \[ \int \frac{2x}{(x^2 + 3)(x^2 - 5)} \, dx \]

Show Hint

Quick Tip: When dealing with rational functions involving quadratics, use partial fraction decomposition to break the function into simpler integrals. This allows you to use standard integral formulas for each term.
Updated On: Jan 13, 2026
Show Solution

Solution and Explanation

To evaluate the integral: \[ \int \frac{2x}{(x^2 + 3)(x^2 - 5)} \, dx \] We apply partial fraction decomposition. The integrand is expressed as: \[ \frac{2x}{(x^2 + 3)(x^2 - 5)} = \frac{A}{x^2 + 3} + \frac{B}{x^2 - 5} \] Multiplying by \( (x^2 + 3)(x^2 - 5) \) yields: \[ 2x = A(x^2 - 5) + B(x^2 + 3) \] Expanding this equation: \[ 2x = A x^2 - 5A + B x^2 + 3B \] Grouping terms by powers of \( x \): \[ 2x = (A + B) x^2 + (-5A + 3B) \] Equating coefficients of like powers of \( x \) on both sides. For \( x^2 \): \[ A + B = 0 \] For \( x \): \[ -5A + 3B = 2 \] Solving the system of equations: From \( A + B = 0 \), we get \( B = -A \). Substituting this into the second equation: \[ -5A + 3(-A) = 2 \] \[ -5A - 3A = 2 \] \[ -8A = 2 \] \[ A = -\frac{1}{4} \] Since \( B = -A \), we find: \[ B = \frac{1}{4} \] The partial fraction decomposition is therefore: \[ \frac{2x}{(x^2 + 3)(x^2 - 5)} = \frac{-1/4}{x^2 + 3} + \frac{1/4}{x^2 - 5} \] Integrating each term: \[ \int \frac{-1/4}{x^2 + 3} \, dx = -\frac{1}{4} \int \frac{1}{x^2 + 3} \, dx = -\frac{1}{4} \cdot \frac{1}{\sqrt{3}} \tan^{-1} \left( \frac{x}{\sqrt{3}} \right) \] \[ \int \frac{1/4}{x^2 - 5} \, dx = \frac{1}{4} \int \frac{1}{x^2 - 5} \, dx = \frac{1}{4} \cdot \frac{1}{\sqrt{5}} \tanh^{-1} \left( \frac{x}{\sqrt{5}} \right) \] The final result of the integration is: \[ \int \frac{2x}{(x^2 + 3)(x^2 - 5)} \, dx = -\frac{1}{4\sqrt{3}} \tan^{-1} \left( \frac{x}{\sqrt{3}} \right) + \frac{1}{4\sqrt{5}} \tanh^{-1} \left( \frac{x}{\sqrt{5}} \right) + C \]
Was this answer helpful?
0