Question 21
Find the coefficient of $x^{6}$ in the expansion of
$$
(x+1)^{6} \cdot \sum_{i=0}^{6} x^{i}
$$
$$
(x+1)^{6} \cdot \sum_{i=0}^{6} x^{i}
$$
MathNet 2008-part-05 — 164 problems (EN–VI) Question 21
Math Olympiad Vault · MathNet 2008-part-05 — 164 problems (EN–VI)