Calculating the Derivative of an Integral Function



Calculating the Derivative of an Integral Function

Question:

If F(x) = \int_{1}^{2x} \frac{1}{1 - t^3} \, dt, then F'(x) =

  • (A) \frac{1}{1 - x^3}
  • (B) \frac{1}{1 - 2x^3}
  • (C) \frac{2}{1 - 2x^3}
  • (D) \frac{1}{1 - 8x^3}
  • (E) \frac{2}{1 - 8x^3}

Step-by-Step Solution

  1. Understand the Function Structure:

    Given the function:

        \[ F(x) = \int_{1}^{2x} \frac{1}{1 - t^3} \, dt \]

    Here, the upper limit of integration is g(x) = 2x.

  2. Apply the Fundamental Theorem of Calculus:

    If F(x) = \int_{a}^{g(x)} f(t) \, dt, then:

        \[ F'(x) = f(g(x)) \cdot g'(x) \]

    Where:

    • f(t) = \frac{1}{1 - t^3}
    • g(x) = 2x
    • g'(x) = 2
  3. Compute F'(x):

        \[ F'(x) = \frac{1}{1 - (2x)^3} \cdot 2 = \frac{2}{1 - 8x^3} \]

  4. Match with the Given Options:

    The derivative simplifies to:

        \[ F'(x) = \frac{2}{1 - 8x^3} \]

    This corresponds to option (E).

Final Answer

Answer: (E) \frac{2}{1 - 8x^3}

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