[Cambridge/9794/Specimen Paper for 2010] Find the value of ∫02x−1x2−2x−3 dx\int_{0}^{2} \frac{x - 1}{x^2 - 2x - 3} \, dx.

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Worked solution

Q3

1. Express the numerator as a scalar multiple of the derivative of the denominator.

Let f(x)=x2−2x−3f(x) = x^2 - 2x - 3.
Then f′(x)=2x−2=2(x−1)f'(x) = 2x - 2 = 2(x - 1).

Therefore, we can rewrite the integral as:
∫02x−1x2−2x−3 dx=12∫022x−2x2−2x−3 dx\int_{0}^{2} \frac{x - 1}{x^2 - 2x - 3} \, dx = \frac{1}{2} \int_{0}^{2} \frac{2x - 2}{x^2 - 2x - 3} \, dx

2. Integrate the function to obtain a natural logarithm, ensuring the use of absolute value symbols.

=[12ln⁡∣x2−2x−3∣]02= \left[ \frac{1}{2} \ln |x^2 - 2x - 3| \right]_{0}^{2}

3. Evaluate the definite integral by substituting the limits.

=12ln⁡∣22−2(2)−3∣−12ln⁡∣02−2(0)−3∣= \frac{1}{2} \ln |2^2 - 2(2) - 3| - \frac{1}{2} \ln |0^2 - 2(0) - 3|

=12ln⁡∣−3∣−12ln⁡∣−3∣= \frac{1}{2} \ln |-3| - \frac{1}{2} \ln |-3|

=12ln⁡3−12ln⁡3= \frac{1}{2} \ln 3 - \frac{1}{2} \ln 3

=0= 0

Answer

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