Use the binomial theorem to find: (a) the coefficient of r4

Last updated: 8/8/2022

Use the binomial theorem to find: (a) the coefficient of r4 in the expansion of (x + 3)²⁰ (b) the sum 1 + 3n +9(n 2) +......+3ᵏ(n k)+...+ 3ⁿ-²(n n-2)+3ⁿ-¹n+ 3ⁿ