x²⁰¹⁹-2019.x²⁰¹⁸+2019.x²⁰¹⁸+2019.x²⁰¹⁷-2019.x²⁰¹⁶+......2019.x-200     Tại x=2018

Giúp mik vs nhé 

Sai đề nên t sửa luôn nhé!

Vì \(x=2018\Rightarrow2019=2018+1=x+1\)

\(A=x^{2017}-2019\cdot x^{2018}+2019\cdot x^{2017}-2019\cdot x^{2016}+....+2019\cdot x-200\)

\(\Rightarrow A=x^{2019}-\left(x+1\right)x^{2018}+\left(x+1\right)x^{2017}-\left(x+1\right)x^{2016}+....-\left(x+1\right)x^2+\left(x+1\right)x-200\)

\(\Rightarrow A=x^{2019}-x^{2019}-x^{2018}+x^{2018}+x^{2017}-x^{2017}-x^{2016}+....-x^3-x^2+x^2+x-200\)

\(\Rightarrow A=x-200=2018-200=1818\)

\(\frac{1}{2}\cdot\frac{2}{3}\cdot\frac{3}{4}...\frac{2018}{2019}\)

\(=\frac{1\cdot2\cdot3\cdot4\cdot\cdot\cdot2018}{2\cdot3\cdot4\cdot5\cdot\cdot\cdot2019}\)

\(=\frac{1\cdot\left(2\cdot3\cdot4\cdot\cdot\cdot2018\right)}{\left(2\cdot4\cdot5\cdot\cdot\cdot2018\right)\cdot2019}\)

\(=\frac{1}{2019}\)

Vậy .......................................

1/2.2/3.3/4.....2018/2019

=1.2.3......2018/2.3.4......2019

=1/2019

\(\frac{1}{2}.\frac{2}{3}.\frac{3}{4}...\frac{2018}{2019}\)

\(=\frac{1.2.3...2018}{2.3.4...2019}\)

\(=\frac{1}{2019}\)

a: 21^15=3^15*7^15

27^5*49^8=3^15*7^14

mà 15>14

nên 21^15>27^5*49^8

b: \(2020^{2020}-2020^{2019}=2020^{2019}\left(2020-1\right)=2020^{2019}\cdot2019\)

\(2020^{2019}-2020^{2018}=2020^{2018}\cdot2019\)

mà 2019>2018

nên 2020^2020-2020^2019>2020^2019-2020^2018

\(A=\dfrac{2020}{2019}-\dfrac{2019}{2018}+\dfrac{1}{2018\times2019}\)

\(A=\dfrac{2020}{2019}-\dfrac{2019}{2018}+\dfrac{1}{2018}-\dfrac{1}{2019}\)

\(A=\left(\dfrac{2020}{2019}-\dfrac{1}{2019}\right)-\left(\dfrac{2019}{2018}-\dfrac{1}{2018}\right)\)

\(A=\left(\dfrac{2020-1}{2019}\right)-\left(\dfrac{2019-1}{2018}\right)\)

\(A=1-1\)

\(A=0.\)

\(A=\dfrac{2020}{2019}-\dfrac{2019}{2018}+\dfrac{1}{2018\times2019}\)

\(A=\dfrac{2020}{2019}-\dfrac{2019}{2018}+\dfrac{1}{2018}-\dfrac{1}{2019}\)

\(A=\left(\dfrac{2020}{2019}-\dfrac{1}{2019}\right)-\left(\dfrac{2019}{2018}-\dfrac{1}{2018}\right)\)

\(A=\dfrac{2019}{2019}-\dfrac{2018}{2018}\)

\(A=1-1\)

\(A=0\)

Mk giúp bn bài 1 thui đc ko 

Bài dưới mk ko bít ~~~~

Sao các bn cứ tk sai mk vô cớ thế nhỉ , mk đã lm j sai , mk chỉ nói là mk ko bít bài 2 thui mak tự nhiên tk ngta sai , bn nào tk mk sai rồi các bn sẽ biết hậu quả thôi :PPP

YuKo à , trước khi gửi câu hỏi phải gửi đoàng hoàng , nếu muốn nói là ko bt làm bài 2 thì gửi tin nhắn nha (rút kinh nghiệm lần sau)

khó quá bẹn gì đấy ơi

M= ( 1/1+1/2+1/3+...+1/2018).(673.3).2.4.5....2018

M= (1/1+1/2+1/3+...+1/2018).2019.2.4.5...2018

vi bieu thuc tren co so 2019

=> M chia het cho 2019

nhầm đề r NGUYỄN BÙI KHÁNH NGỌC ạ