Gọi tông phai tinh la A ta thấy A = (1^2+ 2^2+3^2+4^2+....+ 100^2) - 4x( 1^2+ 2^2+3^2+4^2+....+ 50^2 ) = 100x(100+1)x(2x100+1)/6 - 4x50x(50+1)x(2x50+1)/6 = 166650
(2+4+6+...+100) - (1+3+5+...+99) = ?
1 x 2 + 2 x 3 + 3 x 4 + ... + 99 x 100 = ?
3 x 4 + 4 x 5 + 5 x 6 + ... + 149 x 150 = ?
1 + (1 + 2) + ( 1 + 2 + 3) + (1 + 2 + 3 + 4) + ....... + (1 + 2 + 3 + ... + 99)
----------------------------------------------------------------------------------------------------------- ( gạch ngang phân số )
1 x 99 + 2.98 + 3.97 + ...... + 99 x 1
tính nhanh (2/3+3/4+5/6+...+99/100).(1/2+2/3+3/4+...+98/99)-(1/2+1/3+...+99/100).(2/3+2/4+...+98/99)
1+1+2+2+2+3+3+3+4+4+4+5+5+5+6+6+6+7+7+...+99+99+100
1 + 2 + 3 + 4 + 5 + ... + 99 + 100
2 + 4 + 6 + ... + 2020 + 2022
2/2*5 + 2/5*7 + ... + 2/99*101
1/2 +2/3 +3/4 +4/5+..+99/100
1/99+2/98 +3/97+...+98/2+99/1
help me,ai giải nhanh nhất tớ tick cho
1*2*3+2*3*4+3*4*5+....+97*98*99+98*99*100 = ?
3/1+3/1+2 3/1+2+3+3/1+2+3+4+3/1+2+3+4+5+....+3/1+2+3+4..+99
Tính A:B
a)A=98+1/2+1/3+1/4+...+1/99
B=2/3+4/3+5/4+...+100/99
b)A=2018+1/2+1/3+1/4+...+1/2019
B=3/2+4/3+3/4+...+2020/2019
c)A=99/1+98/2+97/3+...+2/98+1/99
B=1/2+1/3+1/4+...+1/100
Giải đầy đủ
1+2+3+4+5+6+7+8+9+.............+99=X+1+2+3+4+5+6+7+8+9+........................+99
Tìm X
