wait. my question has been changed:
Use the Riemann-Lebesgue Lemma to get the asymptotic expansion of :
$\displaystyle I(m)=\int_{a}^{\infty}{f(t)cos(mt)dt} \ \ \ \ as \ \ \ \ m\rightarrow\infty $
wait. my question has been changed:
Use the Riemann-Lebesgue Lemma to get the asymptotic expansion of :
$\displaystyle I(m)=\int_{a}^{\infty}{f(t)cos(mt)dt} \ \ \ \ as \ \ \ \ m\rightarrow\infty $