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) \(T = C_{2022}^0{4^{2022}} - C_{2022}^1{4^{2021}}.3 + ... - C_{2022}^{2021}{4.3^{2021}} + C_{2022}^{2022}{.3^{2022}}\)
Phương pháp giải - Xem chi tiết
Công thức nhị thức Newton: \({(a + b)^n} = C_n^0{a^n} + C_n^1{a^{n - 1}}b + ... + C_n^{n - 1}a{b^{n - 1}} + C_n^n{b^n}\)
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
\(\begin{array}{l}{\left( {4 - 3} \right)^{2022}} = C_{2022}^0{4^{2022}}.{\left( { - 3} \right)^0} + C_{2022}^1{4^{2021}}.{\left( { - 3} \right)^1} + ...... + C_{2022}^{2021}4.{\left( { - 3} \right)^{2021}} + C_{2022}^{2022}.{\left( { - 3} \right)^{2022}}\\ \Leftrightarrow {1^{2022}} = T = C_{2022}^0{4^{2022}} - C_{2022}^1{4^{2021}}.3 + ... - C_{2022}^{2021}{4.3^{2021}} + C_{2022}^{2022}{.3^{2022}}\\ \Leftrightarrow T = 1\end{array}\)