Evaluate:
∫ − π e 2 ln ( π ) e − x 4 + π cos ( 3 x ) sin ( ( x 3 − π x ) ln ( x 2 + 1 ) ) d x
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This was doing my head in , but then when i looked at it really carefully, I noticed that it is really just zero. It took me 45 minutes to look at it and find the answer lol
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You can plot the integrand to be sure.
The integrand is an odd function, i.e.
f ( x ) = e − x 4 + π cos ( 3 x ) sin ( ( x 3 − π x ) ln ( x 2 + 1 ) )
then
f ( − x ) = e − e ( − x ) 4 + π cos ( 3 ( − x ) ) sin ( ( ( − x ) 3 − π ( − x ) ) ln ( ( − x ) 2 + 1 ) ) = − e − x 4 + π cos ( 3 x ) sin ( ( x 3 − π x ) ln ( x 2 + 1 ) ) = − f ( x )
The integral bounds are − π to e 2 ln ( π ) = e l n ( π ) = π
so
∫ − π e 2 ln ( π ) e − x 4 + π cos ( 3 x ) sin ( ( x 3 − π x ) ln ( x 2 + 1 ) ) d x = 0
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I = ∫ − π exp ( 2 ln π ) e − x 4 + π cos ( 3 x ) sin ( ( x 3 − π x ) ln ( x 2 + 1 ) ) d x = ∫ − π π e − x 4 + π cos ( 3 x ) sin ( ( x 3 − π x ) ln ( x 2 + 1 ) ) d x = 0 Note that e 2 ln π = e ln π = π Numerator is odd while the denominor is even the integrand is odd.