1/2 + 1/6 + 1/12 + 1/20 + 1/30
= 1/1*2 + 1/2*3 + 1/3*4 + 1/ 4*5 + 1/5*6
= 1/1 - 1/2 + 1/2 - 1/3 + 1/4 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6
=1/1 - 1/6
= 6/6 - 1/6
= 5/6
\(tíchnha\) Trương Thị Hoàng Hà
=1/1.2 + 1/2.3 + 1/3.4 .......+1/5.6
=1-1/2 + 1/2-1/3+....+1/5-1/6
=1-1/6
=5/6
= 1/1*2 + 1/2*3 +1/2*4 + 1/4*5 + 1/5*6
=1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 -1/6
=1/1 - 1/6
=6/6 - 1/6
=5/6
\(\frac{30+10+5+3+2}{60}\)
\(\frac{50}{60}\)
\(\frac{5}{6}\)
ta có:
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}\)
\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)
\(=1-\frac{1}{6}\)
\(=\frac{5}{6}\)
1/2+1/6+1/12+1/20+1/30
= 1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6 =
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=
=1-1/6
=5/6
