Question

tinh tong 

D=1.2+2.3+3.4+.....+99.100

 

Answer 1

3B = 1.2.3 + 2.3.3 + 3.3.4 + .... + 3.99.100 
Đặt M = 1.2.3 + 2.3.4 + 3.4.5 + .... + 99.100.101 
=> M - 3A = 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 
=> M -3D = M - 99.100.101 
=> D = 99.100.101/3 = 333300

Answer 2

Bạn nhân cả 2 vế với 3 nhé

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

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

3D=99.100.101

D=99.100.101:3=333300

Answer 3

3B = 1.2.3 + 2.3.3 + 3.3.4 + .... + 3.99.100 
Đặt M = 1.2.3 + 2.3.4 + 3.4.5 + .... + 99.100.101 
=> M - 3A = 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 
=> M -3D = M - 99.100.101 
=> D = 99.100.101/3 = 333300

Answer 4

D = 1.2 + 2.3 + 3.4 +.....+ 99.100

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

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

3D = 99.100.101

D = 99.100.101:3

D = 33.100.101

D=333 300

Vậy D = 333 300