Use this formula only
Find the integral
Of course , little Algebra is allowed . Try to answer this without applying substitution , integration by parts , etc
I just forgot to add this point but actually it is also true when
Although , from the formula , it gives us something like this :
or
the numerator tends to while the denominator tends to zero .
,if we rewrite the constant as , and make very small
so we have
Then use L rule to evaluate the limit , we will find that