S = 12 + 22 + 32 + ..... + 1002
= 1.(2-1) + 2.(3-1) + .... + 100.(101-1)
= 1.2 + 2.3 + ....... + 100.101 - (1+2+3+...+100)
Đặt A = 1.2 + 2.3 + ... + 100.101
3A = 1.2.(3-0) + 2.3.(4-1) + .... + 100.101.(102-99)
3A = 1.2.3 + 2.3.4-1.2.3 + ... +100.101.102-99.100.101
3A = 100.101.102
A = 100.101.102 : 3 = 33367034
S = 33367034 - 5050
S = 33361984
S = 12 + 22 + 32 + ..... + 1002
= 1.(2-1) + 2.(3-1) + .... + 100.(101-1)
= 1.2 + 2.3 + ....... + 100.101 - (1+2+3+...+100)
Đặt A = 1.2 + 2.3 + ... + 100.101
3A = 1.2.(3-0) + 2.3.(4-1) + .... + 100.101.(102-99)
3A = 1.2.3 + 2.3.4-1.2.3 + ... +100.101.102-99.100.101
3A = 100.101.102
A = 100.101.102 : 3 = 33367034
S = 33367034 - 5050
S = 33361984
S = 12 + 22 + 32 + ..... + 1002
= 1.(2-1) + 2.(3-1) + .... + 100.(101-1)
= 1.2 + 2.3 + ....... + 100.101 - (1+2+3+...+100)
Đặt A = 1.2 + 2.3 + ... + 100.101
3A = 1.2.(3-0) + 2.3.(4-1) + .... + 100.101.(102-99)
3A = 1.2.3 + 2.3.4-1.2.3 + ... +100.101.102-99.100.101
3A = 100.101.102
A = 100.101.102 : 3 = 33367034
S = 33367034 - 5050
S = 33361984