Question

Help please!
Which of the following is the third term of the expansion (a + b)^n ?

C(n, 2)a^(n - 2)b^2
C(n, 3)a^(n - 3)b
C(n, 2)a^2b^(n - 2)

Answer 1

a+b)^n = ∑[k = 0 to n] C(n,k) a^(n−k) b^k

Third term: n = 2 -----> C(n,2) a^(n−2) b^2

Answer 2

\[the~~ r^{th} ~~term~~ ~~of~~expansion~~ (a + b)^n~~~is \]
\[(n , r - 1) a^{n - (r - 1)}~b^{r - 1}\]