GCEFurther MathematicsIntegration2019

Using the substitution $u = x^2 + 1$, evaluate $\int_{0}^{2} \frac{x}{x^2+1}\, dx$

A$\ln 5$
B$\frac{1}{2}\ln 5$CORRECT
C$\frac{1}{2}\ln 3$
D$2\ln 5$
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Why the answer is B, and why the others tempt you.
With u = x² + 1, du = 2x dx, so x dx = du/2. When x = 0, u = 1; when x = 2, u = 5. The integral becomes (1/2)∫₁⁵ du/u = (1/2)[ln u]₁⁵ = (1/2)(ln5 - ln1) = (1/2)ln5. Option A omits the factor of 1/2.
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