a] A=1x2 +2x3+3x4+...+ 99x100

b]B=1x100+2x99+3x98+99x2+100x1

c] C=1x1+2x2+3x3+...+100x100









 

C=1x100+2x99+3x98+...+99x2+100x1 = ?

tính nhanh : S= 1x100 +  2x99 + 3x98 + .... + 98x3 + 99x2 + 100x1

1+(1+2)+(1+2+3)+...+(1+2+...+100) /1x100+2x99+3x98+...+100x1

Tinh nhanh 

F = 1x100+2x99+3x98+....+98x3+100x1

1+(1+2)+(1+2+3)+. . .+(1+2+3+...+100) / 1x100+2x99+3x98+...+100x1

Tính nhanh:

1+(1+2)+(1+2+3)+(1+2+3+4)+.......+(1+2+3+...+100)/100x1+99x2+98x3+.........+2x99+1x100.

Rút gọn tổng sau một cách hợp lí :

a, A = 5^2 + 5^4 + 5^6 + ... + 5^2020

b, 1x100 + 2x99 + 3x98 + 4x97 + .... + 100x1

Tính nhanh:

\(\frac{1+(1+2)+(1+2+3)+(1+2+3+4)+.......+(1+2+3+...+100)}{100x1+99x2+98x3+.........+2x99+1x100}\)