Question

2	+	2	+ … +	2	=
3 x 5		5 x 7		111 x 113

Answer 1

Ta có: \(\dfrac{2}{3\cdot5}+\dfrac{2}{5\cdot7}+...+\dfrac{2}{111\cdot113}\)

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

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

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

Answer 2

2/3x5 + 2/5x7 + ....+2/111x113

=1/3-1/5 + 1/5 - 1/7 +....+1/111-1/113

=1/3 - 1/113

=110/339