P = ∫ 0 ∞ e − π x x sin x d x Find the value of ⌊ 1 0 0 P ⌋ .
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No need to use such tranformations.
Just use expansion of sin(x) and gamma function and few skills of integration
∫ 0 ∞ e − π x x sin x d x = 2 i 1 ∫ 0 ∞ x e − ( π − i ) x − x e − ( π + i ) x d x
Individually each integral cannot be evaluated like a Gaussian because Γ ( 0 ) = ∞ (below)
∫ 0 ∞ x b e − a x n d x = a n b + 1 n 1 Γ ( n b + 1 )
Using Feynman's trick: I ( a ) = ∫ 0 ∞ x e − a x − 1 = − ln a + C , the original integral becomes:
ℜ ( 2 i ln ( π − i π + i ) ) = ℜ ( i ln ( π + i ) ) = arctan π 1
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Using Laplace transformation
L ( x sin x ) = ∫ s ∞ s 2 + 1 1 d s
L ( x sin x ) = arctan ∣ s ∞
s = π
⇒ L ( x sin x ) = arccot ( π )
⌊ 1 0 0 a r c c o t ( π ) ⌋ = 3 0