Question

[zai vlogs]

tính

2/3+2/15+2/35+2/63+2/99

1/1×2+1/2×3+1/3×4+..........+1/1995×1996+1/1996×1997

Answer 1

[Vũ Hải Lâm]

2/\(\frac{10}{11}\)

Answer 2

[Nguyễn Kim Ngân]

câu 1:

\(\frac{2}{3}+\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}\)

\(\hept{\begin{cases}15=3\cdot5\\35=5\cdot7\end{cases}}\\ \hept{\begin{cases}3=3\\63=3^2\cdot7\\99=3^2\cdot11\end{cases}}\)

=>\(\frac{2310}{3465}+\frac{462}{3465}+\frac{198}{3465}+\frac{110}{3465}+\frac{70}{3465}\)

=>\(\frac{2310+462+198+110+70}{3465}\)

=>\(\frac{3150}{3465}\)=\(\frac{10}{11}\)