What is the limit of xsinxxsinx as x approaches infinity?

1 Answer
Jul 18, 2016

The limit does not exist. See below.

Explanation:

We can determine the result by pure intuition.

We know that sinxsinx alternates between -11 and 11, from negative infinity to infinity. We also know that xx increases from negative infinity to infinity. What we have, then, at large values of xx is a large number (xx) multiplied by a number between -11 and 11 (due to sinxsinx).

This means the limit does not exist. We do not know if xx is being multiplied by -11 or 11 at oo, because there is no way for us to determine that. The function will essentially alternate between infinity and negative infinity at large values of xx. If, for example, xx is a very large number and sinx=1sinx=1, then the limit is infinity (large positive number xx times 11); but (3pi)/23π2 radians later, sinx=-1sinx=1 and the limit is negative infinity (large positive number xx times -11).