A=11.2.3+12.3.4+13.4.5+...+198.99.100=11.2−12.3+12.3−13.4+...+198.99−199.100=11.2−199.100=494919800
A=11.2.3+12.3.4+13.4.5+...+198.99.100=11.2−12.3+12.3−13.4+...+198.99−199.100=11.2−199.100=494919800
1/1.2.3 + 1/2.3.4 + 1/3.4.5+...+1/98.99.100 = ?
tính: 1/1.2.3+1/2.3.4+1/3.4.5+...+1/98.99.100
Tính:
B=1/1.2.3+1/2.3.4+1/3.4.5+............+1/98.99.100
Tính A = 1/1.2.3 + 1/2.3.4 + 1/3.4.5 + ............. + 1/ 98.99.100
1/1.2.3 +1/2.3.4+1/3.4.5+...+1/98.99.100 = ( 1/k . 1/99.100)
Tính : a, 1.2.3 + 2.3.4 + 3.4.5 + ... + (n - 1).n.(n+1)
b, 1.2.3 + 3.4.5 + 5.6.7 + 98.99.100
C= 1 phần 1.2.3+1 phần 2.3.4+1 phần 3.4.5+..........+1 phần 98.99.100
tìm y biết :
a) (1/1.2.3+1/2.3.4+1/3.4.5+...+1/98.99.100)
Tìm x (1/1.2.3+1/2.3.4+1/3.4.5+...+1/98.99.100).x=49/200