Giải bài 2 trang 37 Chuyên đề học tập Toán 10 – Cánh diều — Không quảng cáo

Đề bài

Tính:

a) $S = C_{2022}^0{9^{2022}} + C_{2022}^1{9^{2021}} + ... + C_{2022}^k{9^{2022 - k}} + ... + C_{2022}^{2021}9 + C_{2022}^{2022}$

b) $T = C_{2022}^0{4^{2022}} - C_{2022}^1{4^{2021}}.3 + ... - C_{2022}^{2021}{4.3^{2021}} + C_{2022}^{2022}{.3^{2022}}$

Lời giải chi tiết

a) Theo công thức nhị thức Newton, ta có: ${\left( {9 + x} \right)^{2022}} = C_{2022}^0{9^{2022}}.{x^0} + C_{2022}^1{9^{2021}}.{x^1} + ... + C_{2022}^k{9^{2022 - k}}.{x^k} + ... + C_{2022}^{2021}9.{x^{2021}} + C_{2022}^{2022}.{x^{2022}}$

Thay $x = 1$ ta được: ${\left( {9 + 1} \right)^{2022}} = S = C_{2022}^0{9^{2022}} + C_{2022}^1{9^{2021}} + ... + C_{2022}^k{9^{2022 - k}} + ... + C_{2022}^{2021}9 + C_{2022}^{2022} \Rightarrow S = {10^{2022}}$

b) Theo công thức nhị thức Newton, ta có:

${\left( {4 + x} \right)^{2022}} = C_{2022}^0{4^{2022}}.{x^0} + C_{2022}^1{4^{2021}}.{x^1} + ... + C_{2022}^k{4^{2022 - k}}.{x^k} + ... + C_{2022}^{2021}4.{x^{2021}} + C_{2022}^{2022}.{x^{2022}}$

Thay $x =  - 3$ ta được

$\begin{array}{l}{\left( {4 - 3} \right)^{2022}} = C_{2022}^0{4^{2022}}.{\left( { - 3} \right)^0} + C_{2022}^1{4^{2021}}.{\left( { - 3} \right)^1} + ...... + C_{2022}^{2021}4.{\left( { - 3} \right)^{2021}} + C_{2022}^{2022}.{\left( { - 3} \right)^{2022}}\\ \Leftrightarrow {1^{2022}} = T = C_{2022}^0{4^{2022}} - C_{2022}^1{4^{2021}}.3 + ... - C_{2022}^{2021}{4.3^{2021}} + C_{2022}^{2022}{.3^{2022}}\\ \Leftrightarrow T = 1\end{array}$