đặt 5^2+...+5^1997

=5A-A=5^3+...+5^1998 - 5^2-...- 5^1997

= 4A= 5^1998-5^2

=5^1998-5^2/4

A=6+5²+5³+5⁴+...+5¹⁹⁹⁶+5¹⁹⁹⁷

A = 1 + 5 + 5² + 5³ + ... + 5¹⁹⁹⁶ + 5¹⁹⁹⁷

5A = 5 + 5² + 5³ + 5⁴ + ... + 5¹⁹⁹⁷ + 5¹⁹⁹⁸

5A - A = ( 5 + 5² + 5³ + 5⁴ + ... + 5¹⁹⁹⁷ + 5¹⁹⁹⁸ ) - ( 1 + 5 + 5² + 5³ + ... + 5¹⁹⁹⁶ + 5¹⁹⁹⁷ )

4A = 5¹⁹⁹⁸ - 1

\(\Rightarrow A=\frac{5^{1998}-1}{4}\)

\(A=6+5^2+5^3+...+5^{1996}+5^{1997}\\ A=1+5+5^2+5^3+...+5^{1996}+5^{1997}\)

\(5A=5+5^2+5^3+...+5^{1996}+5^{1998}\)

\(5A-A=\left(5+5^2+5^3+...+5^{1996}+5^{1998}\right)-\left(1+5+5^2+5^3+...+5^{1996}+5^{1997}\right)\)

\(4A=5^{1998}-1\\ A=\frac{5^{1998}-1}{4}\)

1. M lớn nhất khi m nhỏ nhất=> m=1 (vì m phải khác 0 phép chia mới có nghĩa) 

Khi đó M=10020 

Vậy..........

de bieu thuc co gia tri lon nhat thi so do phai be nhat 

do khac 0 va so do phai be nhat thi M se lon nhat . Nho nhat chi co the la 1

vay m la 1 

Neu dung cac ban cho minh 1 h nhe

a) A=1-2-3+4+5-6-7+.....+1996+1997-1998-1999+2000

=(1-2-3+4)+(5-6-7+8)+...+(1997-1998-1999+2000)

=0

b) B=1-3+5-7+....+2001-2003+2005

=(1-3)+(5-7)+...+(2001-2003)+2005

=-2.501+2005

=-1002+2005

=1003

c) C=1-2-3+4+5-6-7+8+.....+1993-1994-1995+1996+1997

=(1-2-3+4)+(5-6-7+8)+...+(1993-1994-1995+1996)+1997

=1997

d) D=1000+998+996+......+10-999-997-995-...-11

=(1000-999)+(998-997)+(996-995)+....+(12-11)+10

=1.495+10

=595

Ta có: \(A=6+5^2+5^3+5^4+...+5^{1996}+5^{1997}=1+5+5^2+5^3+...+1^{1997}\)

\(\Rightarrow5A=5+5^2+5^3+5^4+...+5^{1997}+5^{1998}\)

\(\Rightarrow5A-A=\left(5+5^2+5^3+5^4+...+5^{1997}+5^{1998}\right)-\left(1+5+5^2+5^3+...+5^{1996}+5^{1997}\right)\)

\(\Rightarrow4A=5^{1998}-1\Rightarrow A=\dfrac{5^{1998}-1}{4}\)

Vậy ...