A=1.2+2.3+3.4+...+99.100

=>3A=1.2.3+2.3.3+3.4.3+...+99.100.3

=1.2.3+2.3(4-1)+3.4(5-2)+....+99.100(101-98)

=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+99.100.101-98.99.100

=99.100.101=999900

=>A=333300

vậy A=333300

l-i-k-e cho mình nha

Ta có : M = 1 . 2 + 2 . 3 + 3 . 4 + ........+ 99 . 100

         3M = 1 . 2 . 3 + 2 . 3 . ( 4 - 1 ) + 3 . 4 . ( 5 - 2 ) + ..........+ 99 . 100 . ( 101 - 98 )

         3M = 1 . 2 . 3 + 2 . 3 . 4 - 1. 2 . 3 + 3 . 4 . 5 - 2 . 3 . 4 + ..........+ 99 . 100 . 101 -  98 . 99 . 100

         3M = 99 . 100 . 101

          M = 33 . 100 . 101 = 333300

Đúng nha !!!

Ta có:

M=1.2+2.3+3.4+....+99.100

3M=1.2.3+2.3.(4-1)+3.4.(5-2)+...+99.100.(101-98)

3M=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+....+99.100.101-98.99.100

M=99.100.101  = 333300

           3

  A=1.2+ 2.3+.......+99.100 
Nhân cả 2 vế với 3, ta được: 
3A=1.2.3+ 2.3.3+ 3.4.3+ 4.5.3+...... 99.100.3 
= 1.2.3 + 2.3(4-1) + 3.4.(5-2) +...+ 99.100.(101-98) 
= 1.2.3 + 2.3.4 -1.2.3 + 3.4.5-2.3.4 +...+ 99.100.101-98.99.100 
= 99.100.101 
----> A = (99.100.101):3 
A = 333300 
Vậy A=333300 

gọi tổng là S ta có

3S=1.2.3-0.1.2+2.3.4-1.2.3+....+99.100.101-98.99.100

=>3s=99.100.101

=>S=99.100.101:3=333300

gọi tổng là S ta có

3S=1.2.3-0.1.2+2.3.4-1.2.3+......+99.100.101-98.99.100

=>3S=98.99.100

=>S=\(\frac{98.99.100}{3}=323400\)

333300

=>3C=1.2.3+2.3.3+...+99.100.3

= 1.2.(3 - 0) + 2.3.(4 - 1) +...+ 99.100.(101 - 98)

= 1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 +...+ 99.100.101 - 98.99.100

= 99.100.101

=>\(C=\frac{99.100.101}{3}=333300\)

\(C = 1.2+2.3+3.4+...+99.100\)

\(\Rightarrow3C=1.2.3+2.3.3+3.4.3+...+99.100.3\)

\(3C=1.2.\left(3-0\right)+2.3.\left(4-1\right)+3.4.\left(5-2\right)+...+99.100.\)\(\left(101-98\right)\)

\(3C=\left(1.2.3+2.3.4+3.4.5+...+99.100.101\right)\)\(-\left(0.1.2+1.2.3+2.3.4+...+98.99.100\right)\)

\(3C=99.100.101-0.1.2\)

\(3C=999900-0=999900\)

\(C=999900:3\)

\(\Rightarrow C=333300\)

Ta có: 3A=1.2.3+2.3.3+3.4.3+.....+99.100.3

3A=1.2.3+2.3.(4-1)+3.4..(5-2)+....+99.100.(101-98)

3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+....+99.100.101-98.99.100

3A=99.100.101

A=\(\frac{99.100.101}{3}\)

A=333300

Đặt A= 1.2+2.3 +.......+99.100

3A= 1.2.3+2.3.4+3.4.3 +......+ 99.100.3

3A= 1.2. (3 - 0) + 2.3.(4 - 1) +3.4. (5 - 2)....... . 99.100. (101 - 98)

3A = (1.2.3 + 2.3.4 + 3.4.5 +...... + 99.100.101) - (0.1.2 + 1.2.3 + 2.3.4 +.......+ 98.99.100)

3A = 99.100.101 - 0.1.2

3A = 999900 - 0

3A= 999900

A= 999900 : 3

A = 333300

3A=1×2×3+2×3×3+3×4×3+...+99×100×3

3A=1×2×(3-0)+2×3×(4-1)+3×4×(5-2)+...+99×100×(101-98)

3A=1×2×3 + 2×3×4 - 2×3×1 + 3×4×5 - 3×4×2 +...+ 99×100×101 - 99×100×98

3A=99×100×101

=>A=99×100×101/3=333300

Tk mình nha bn !

3Z = 1.2.3 + 2.3.3 + 3.3.4 + .... + 3.99.100 
 Z= 1.2.3 + 2.3.4 + 3.4.5 + .... + 99.100.101 
=> Z - 3Z = 1.2.3 - 1.2.3 + 2.3.(4-3) + 3.4 ( 5-3) + .... + 99.100 ( 101 -3) 
= 1.2.3 + 2.3.4 + .... + 98.99.100 
=> Z -3Z = Z - 99.100.101 
=> Z  = 99.100.101/3 = 333300

\(Z=1.2+2.3+3.4+...+99.100\)

\(3Z=1.2.3+2.3.\left(4-1\right)+3.4.\left(5-2\right)+...+99.100.\left(101-98\right)\)

\(3Z=1.2.3+2.3.4-1.2.3+3.4.5-2.4.5+...+99.100.101-98.99.100\)

\(3Z=99.100.101\)

\(Z=\frac{99.100.101}{3}=\frac{999900}{3}=333300\)

Z = 1.2 + 2.3 + 3.4 + ......... + 99.100

1/Z = 1/1.2 + 1/2.3 + 1/3.4 + .......... + 1/99.100

1/Z = 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ..... + 1/99 - 1/100

1/Z = 1/1 - 1/100

1/Z = 1/1 - 1/100

1/Z = 99/100

Z = 100/99

A= 1.2 +2.3+ 3.4 +4.5+...+ 99.100 
3A = 1.2.3 +2.3.3+ 3.4.3+...+99.100.3 
3A = 1.2.3 +2.3(4-1)+ 3.4(5-2)+...+99.100(101-98) 
3A = 1.2.3 +2.3.4-1.2.3+ 3.4.5-2.3.4+...+99.100.101-98.99.100 
3A = 999900 
A = 333300

A= 1. 2 + 2.3 +3.4 + 4.5 + 99.100

A=2 +6+12+20 + 9900

A = 9930 

bn nha 

tk mk nha 

A=1.2+2.3+3.4+4.5+99.100

A=101x101x102:3

A=343400

k nha