Calculus · Integrals

How to Find an Antiderivative

Problem

∫3x2 dx\int 3x^2\,dx

Answer

x3+Cx^3 + C

An antiderivative reverses a derivative. The power rule for integrals raises the power by one and divides by the new power.

Step-by-step solution

  1. Write the power rule for integrals.

    ∫xn dx=xn+1n+1+C\int x^n\,dx = \frac{x^{n+1}}{n+1} + C

    Why: The rule reverses the power rule for derivatives.

  2. Apply the rule with n = 2.

    ∫3x2 dx=3⋅x33+C\int 3x^2\,dx = 3 \cdot \frac{x^3}{3} + C

    Why: The power rises to 3 and the coefficient divides by the new power.

  3. Simplify.

    x3+Cx^3 + C

    Why: The 3 on top and the 3 on the bottom cancel.

Common mistakes

  • Forgetting the constant C. Every antiderivative can have one.
  • Subtracting one from the power instead of adding one.
  • Multiplying by the new power instead of dividing.

Practice problems

Use the same method. Work each problem on paper, then open the answer to check.

  1. ∫x dx\int x\,dx

    Show answer

    x22+C\frac{x^2}{2} + C

  2. ∫2x dx\int 2x\,dx

    Show answer

    x2+Cx^2 + C

  3. ∫x2 dx\int x^2\,dx

    Show answer

    x33+C\frac{x^3}{3} + C

  4. ∫4x3 dx\int 4x^3\,dx

    Show answer

    x4+Cx^4 + C

  5. ∫5 dx\int 5\,dx

    Show answer

    5x+C5x + C