Question

1.2+2.3+3.4+.....+99.100

tính tổng

Answer 1

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 

Answer 2

Goi tong tren la A 

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

=>3A=1.2.3+2.3.3+3.3.4+....+99.100.3

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

=1.2.3-0.1.2+2.3.4-1.2.3+3.4.5-2.3.4+...+99.100.101-98.99.100

=99.100.101-0

=999900

=>A=999900:3

A=333300

Answer 3

Gọi biểu thức trên là A, ta có :

A = 1.2 + 2.3 + 3.4 + 4.5 + ...+ 99.100

A . 3 = 1.2.3 + 2.3.3 + 3.4.3 + 4.5.3 + ... + 99.100.3

A . 3 = 1.2.3 + 2.3.(4-1) + 3.4.(5-2) + 4.5.(6-3) + ... + 99.100.(101-98)

A . 3 = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + 4.5.6 - 3.4.5 + ... + 99.100.101 - 98.99.100.

A . 3 = 99.100.101

A = 99.100.101 : 3

A = 333300

Answer 4

Đặt 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

=(1.2.3-1.2.3)+(2.3.4-2.3.4)+...+(98.99.100-98.99.100)+99.100.101

=99.100.101

=999900

.=>A=999900/3=333300

Answer 5

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 

Answer 6

Bài này có trong Violympic lớp 5 đấy. Kết quả là 5003,55 chắc chắn 100% luôn

Answer 7

333300

Answer 8

A=33300 nha dung

Answer 9

1.2 +2.3+3.4+...+99.100

3S= 1.2.3+2.3.3+3.4.4+...+99.100.3

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

3S= 1.2.3-1.2.0+2.3.4-1.2.3+3.4.5-2.3.4+....+99.100.101- 98.99.100

3S =99.100.101 \(\Rightarrow\)99.100.101 : 3 =333 300