A = 1/2 - 1/3 - 1/4 + 1/3 - 1/4 - 1/5 + 1/4 - 1/5 - 1/6
A = 1/2 - 1/6
A = 1/3
k mk nha. ths bn nhìu nha
A = 1/2.3 - 1/ 3.4 + 1/3.4 - 1/4.5 + 1/4.5 -1/5.6
= 1/2.3 - 1/5.6
= 1/6 - 1/30
= 2/15
Vậy A = 1/15
Tính nhanh: \(\frac{-1}{2.3.4}+\frac{-1}{3.4.5}+\frac{-1}{4.5.6}+...+\frac{-1}{28.29.30}\)
tính \(\frac{1}{2.3.4}+\frac{1}{3.4.5}+\frac{1}{4.5.6}+\frac{1}{5.6.7}+\frac{1}{6.7.8}+\frac{1}{7.8.9}+\frac{1}{8.9.10}\)
\(\frac{3x}{5}=\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+\frac{1}{4.5.6}+\frac{1}{5.6.7}+\frac{1}{6.7.8}\).
Tính nhanh :
C = \(\frac{3}{2.3.4}+\frac{3}{3.4.5}+\frac{3}{4.5.6}+....+\frac{3}{98.99.100}\)
Tính nhanh:
\(A=\frac{1}{1.2.3}-\frac{1}{2.3.4}-\frac{1}{3.4.5}-...-\frac{1}{97.98.99}\)
Tính nhanh
\(\frac{1}{2.3.4}+\frac{1}{4.5.6}+...+\frac{1}{20.21.22}\)
Tính nhanh\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{37.38.39}\)
\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{37.38.39}\)
Tính nhanh
Tinh nhanh :
\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{98.99.100}\)
