1 + 2 + 3 + ... + 98 + 99
= (1 + 99) x 99 : 2
= 100 x 99 : 2
= 50 x 99
= 4950
Có số số hạng là:
(99-1):1+1=99
Tổng Là:
(99+1)x99:2=4950
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
Tính \(T=\left(\frac{2}{98}+\frac{3}{97}+...+\frac{99}{1}\right)X\left(\frac{1}{99}+\frac{2}{98}+...+\frac{98}{2}\right)-\left(\frac{1}{99}+\frac{2}{98}+..+\frac{99}{1}\right)X\left(\frac{2}{98}+\frac{3}{97}+...+\frac{98}{2}\right)\)
101+100+99+98+...+3+2+1/101-100+99-98+...+3-2+1
tinh 1*99+2*98+3*97+....+98*2+99*1
Tính M/N biết M = 99/1 + 98/2 + 97/3 + ... + 2/98 + 1/99 và N = 1/2 + 1/3 + 1/4 +...+1/99+1/100
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
1*2*3+2*3*4+...+97*98*99+98*99*100 = ?
-1 / 100 . 99 - 1 / 99 . 98 - 1 / 98 . 97 - ... -1 / 3 . 2 - 1 / 2 . 1
