1+2+3+ ...+98+99+100 = 5050
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B=3^100-3^99-3^98-..-3-1
B=3^100-(3^99+3^98+...+3+1)
ta có:M=3^99+3^98+..+3+1
3M=3^100+3^98+...+3^2+3
2M=3M-M=3^100+3^99+3^98+...+3^2+3-3^99+3^98+...+1
2M=3^100-1
=>B=3^100-3^100+1:2
B=0+1/2
B=1/2
101+100+99+98+...+3+2+1/101-100+99-98+...+3-2+1
B=(101+100+99+98+.....+3+2+1) / (101-100+99-98+.......+3-2+1)
B=(101+100+99+98+.....+3+2+1) / (101-100+99-98+.......+3-2+1)
A=101+100+99+98+...+3+2+1/101-100+99-98+...+3-2+1
Tính : C=101+100+99+98+...+3+2+1 phần101-100+99-98+...+3-2+1
101 +100+99+98+.........+3+2+1
101-100+99+98+.....+3-2+1
101+100+99+98+...+3+2+1
101-100+99-98+...+3-2+1
Rút gọn S=101+100+99+98+...+3+2+1 :101-100+99-98+...+3-2+1
C= 1/100 -1/100×99 -1/99×98 -1/98×97-...-1/3×2 - 1/2×1