Does the following integral converge or diverge?
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We will use the comparison theorem to prove this. Let f ( x ) = e x + 1 arctan ( x ) We know the maximum value arctan ( x ) can take is 2 π , therefore we can set an upper bound of f ( x ) as 2 e x + 2 π . If we can prove that this is less than a function g ( x ) for all x > 0 then we have consequently shown that f ( x ) < g ( x ) for all x > 0 . If this is the case, and if g ( x ) converges, then f ( x ) must also converge. We now let g ( x ) = e x π , since we know ∫ 0 ∞ e x π = π . Now with a little rearranging, it is clear that 2 e x + 2 π < e x π and therefore the integral must converge.