If it only touches the x-axis but doesn't go through it, the Zero function won't work.
What you need to do instead is go to your Y= screen and set Y[SIZE="1"]2[/SIZE] equal to zero.
Y[SIZE="1"]1[/SIZE]= Your equation
Y[SIZE="1"]2[/SIZE]= 0
Then go to 2nd Trace - then use "Intersect" (5). Move the cursor in your first function (Y[SIZE="1"]1[/SIZE]) over near where you think it's touching the x-axis. Then just hit enter twice.
It should tell you the exact zero. If it doesn't, then you know that the graph doesn't even touch the x-axis.