A = 1x2 + 2x3 + 3x4 + 4x5 + ...+ 99x100
A x 3 = 1x2x3 + 2x3x3 + 3x4x3 + 4x5x3 + ... + 99x100x3 A x 3 = 1x2x3 + 2x3x(4-1) + 3x4x(5-2) + 4x5x(6-3) + ... + 99x100x(101-98) ..................................
A x 3 = 99x100x101 A = 333300
Tính nhanh:.
A = 1x2 + 2x3 + 3x4 + 4x5 + ... + 99x100.
tinh nhanh A = 1x2 + 2x3 + 3x4 + 4x5 +.............+ 99x100
Tính:
A=1x2+2x3+3x4+4x5+......+99x100+100x101
tinh nhanh 2/1X2+2/2X3 +2/3X4+2/4X5 + ............ +2/99X100
A=1x2+2x3+3x4+4x5+...+99x100
1x2 + 2x3 + 3x4 + 4x5 + .... +99x100
tính:2/1x2+2/2x3+2/3x4+2/4x5+...+2/99x100
S= 1x2+2x3+3x4+4x5+...+98x99+99x100
tính nhanh
\(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+....+\frac{1}{99x100}\)
