Question

2/5x6 +2/6x7 + ... + 2/68x69

giúp mình vs

ai nhanh mình tick cho

:)

Answer 1

mình cần gấp

Answer 2

\(\frac{2}{5\times6}+\frac{2}{6\times7}+...+\frac{2}{68\times69}\)

\(=\left(\frac{1}{5\times6}+\frac{1}{6\times7}+...+\frac{1}{68\times69}\right)\times2\times\frac{1}{2}\)

\(=\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{68}-\frac{1}{69}\right)\times1\)

\(=\left(\frac{1}{5}-\frac{1}{69}\right)\times1\)

\(=\frac{64}{345}\times1=\frac{64}{345}\)

#Nii