Question

Giúp mk đi chiều nay kt rồi

Answer 1

a.

\(\frac{1}{2\times3}=\frac{1}{6}\)

\(\frac{1}{2}-\frac{1}{3}=\frac{3}{6}-\frac{2}{6}=\frac{1}{6}\)

\(\Rightarrow\frac{1}{2\times3}=\frac{1}{2}-\frac{1}{3}\)

b.

\(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+.....+\frac{1}{2005\times2006}\)

\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+.....+\frac{1}{2005}-\frac{1}{2006}\)

\(=1-\frac{1}{2006}\)

\(=\frac{2005}{2006}\)

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