How do I expand this equation: $(1+t+t^2)^5$
I formed the equation into a binomial equation this way: $(1+t+t^2)^5=\sum \binom{5}{r_1}\binom{5-r_1}{r_2}t^{r_2}t^{2r_1}$
But I cannot remember how to continue from here to solve for the $r_1$ and $r_2$ terms from here and then to further expand it.
Thanks for any help!