On any downward-sloping linear demand curve, there are some points on the curve where demand is elastic, some points where it is inelastic, and one point where it is unit elastic.
Without even doing any math or knowing the exact formula for the demand curve, we can already figure out that the elastic part of the demand curve occurs on the left side of the demand curve. That is, at low quantities. Similarly, the inelastic part of the demand curve occurs at high quantities. It looks like this:
How do we know this?