Answer
See prove below.
Work Step by Step
1. List all possible rational zeros as $\pm1,\pm2$
2. Use remainder theorem or synthetic division to test the above values
$P(1)=1-1-2=-2, P(-1)=-1+1-2=-2, P(2)=8-2-2=4,P(-2)=-8+2-2=-8$
3. As the values in the list are not zeros, we conclude that there are no rational zeros.