Q.24 - Integration

Calculus Level 4

{ ln A = 0 1 x 1 ( x + 1 ) ln x d x B = A A sin x + cos x d x \begin{cases} \begin{aligned} \ln A & = \int_{0}^{1} \frac{x-1}{(x+1) \ln x}\ \mathrm{d}x \\ B & = \int_{-A}^{A} \sin|x| + \cos|x|\ \mathrm{d}x \end{aligned} \end{cases}

Find B B .


The answer is 4.

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1 solution

William Ly
Dec 2, 2020

Outline for one solution: To solve the first integral, expand 1/(1+x) as a geometric series and use a special case of the Frullani integral. Then use the Wallis product to solve for A. Next, solve the second integral. Split the integral to remove the absolute values.

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