could anyone solve this integral ?
∫∞0e−xsin(x)cos(ax)x dx
well i have tried opening up the sin*cos using trigonometric identities but that didn't help so much
Answer
By the sine addition formulas, it is enough to compute
f(m)=∫+∞0sin(mx)xe−xdx
where f(0)=0 and by the dominated convergence theorem
f′(m)=∫+∞0cos(mx)e−xdxIBP=11+m2
implying:
f(m)=∫+∞0sin(mx)xe−xdx=arctan(m)
and
∫+∞0sin(x)cos(ax)xe−xdx=arctan(1−a)+arctan(1+a)2=12arctan2a2.
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