The equation above holds true for positive integers , , and , where and are coprime. Find the value of .
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Substituting e x 2 − 1 = t the integral changes to
∫ 0 1 t ln ( 1 + t ) d t
= ∫ 0 1 n = 1 ∑ ∞ n ( − t ) n − 1 d t
= n = 1 ∑ ∞ ( ∫ 0 1 n ( − t ) n − 1 d t )
= n = 1 ∑ ∞ n 2 ( − 1 ) n − 1
= ( n = 1 ∑ ∞ n 2 1 ) − ( 2 1 n = 1 ∑ ∞ n 2 1 )
= 1 2 π 2
Thus, making the answer 1 ⋅ 2 ⋅ 1 2 = 2 4
Note
n = 1 ∑ ∞ n 2 1 = 6 π 2 follows from the Riemann Zeta Function