S = 12 + 22 + 32 + ....+ 1002
S = 1.(2-1) + 2(3-1) + ... + 100.(101 - 1)
S = 1.2 + 2.3 + .... + 100.101 - (1 + 2+ 3 +........ + 100)
Đặt A = 1.2 + 2.3 + ..... + 100.101
3A = 1.2.3 + 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 = 3367034
Thay vào được
S = A - 100 x 101 : 2
S = 3367034 - 5050 = 3361984
S=1^2+2^2+3^2+.....+100^2
S=1+2.(1+1)+3.(2+1)+.....+99.(98+1)+100.(99+1)
S=1+2.1+2+3.2+3+.....+99.98+99+100.99+100
S=(1.2+2.3+3.4+...+98.99+99.100)+(1+2+3+4+....+99+100)
S=333300+5050
S=338050
tick nha
S=1.(2-1)+2.(3-1)+..........+100.(101-1)
S=1.2-1+2.3-2+...........+100.101-100
S=(1.2+2.3+.............+100.101)-(1+2+.........+100)
Gọi ve 1 của S la:a
3a=1.2.3+2.3.(4-1)+...........+100.101.(102-99)
3a=1.2.3+2.3.4-1.2.3+........+100.101.102-99.100.101
a=100.101.102:3
a=343400
S=343400-[100.(100+1):2]
S=343400-5050
S=338350
S=1^2+2^2+3^2+.....+100^2
S=1+2.(1+1)+3.(2+1)+.....+99.(98+1)+100.(99+1)
S=1+2.1+2+3.2+3+.....+99.98+99+100.99+100
S=(1.2+2.3+3.4+...+98.99+99.100)+(1+2+3+4+....+99+100)
S=333300+5050
S=338050
tick nha
S=1^2+2^2+3^2+.....+100^2
S=1+2.(1+1)+3.(2+1)+.....+99.(98+1)+100.(99+1)
S=1+2.1+2+3.2+3+.....+99.98+99+100.99+100
S=(1.2+2.3+3.4+...+98.99+99.100)+(1+2+3+4+....+99+100)
S=333300+5050
S=338050
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