Question

[꧁༺bủn༻꧂ (ɻɛɑm ʙáo cáo) + ( Team M A...]

 

2	+	2	+ … +	2	=
3 x 5	5 x 7	111 x 113

Answer 1

[Đoàn Đức Hà]

\(\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{111\times113}\)

\(=\frac{5-3}{3\times5}+\frac{7-5}{5\times7}+...+\frac{113-111}{111\times113}\)

\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{111}-\frac{1}{113}\)

\(=\frac{1}{3}-\frac{1}{113}\)

\(=\frac{110}{339}\)