Question

[Nguyễn Anh Thiện]

\(\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\cdot x=1\)

Answer 1

[Phúc Nguyễn]

=> 2(1/15+1/35+1/63+1/99)x=2

=>(1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)x=2

=>8/33x=2

=>x=2:8/33

=>x=8,25

Answer 2

[Đức Phạm]

\(\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\cdot x=1\)

\(\left(\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+\frac{1}{7\cdot9}+\frac{1}{9\cdot11}\right)\cdot x=1\)

\(\left[\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\right]\cdot x=1\)

\(\left[\frac{1}{2}\left(\frac{1}{3}-\frac{1}{11}\right)\right]\cdot x=1\)

\(\left[\frac{1}{2}\cdot\frac{8}{33}\right]\cdot x=1\)

\(\frac{4}{33}\cdot x=1\)

\(\Rightarrow x=\frac{1}{\frac{4}{33}}=\frac{33}{4}\)