Cho x là số thỏa mãn x+ 4/5.9+ 4/ 9.13+ 4/ 13/17+....+ 4/ 41.45=-37/45

* Hướng dẫn giải

$x+\frac{4}{5.9}+\frac{4}{9.13}+\frac{4}{13.17}+\mathrm{...}+\frac{4}{41.45}=\frac{-37}{45}$

$x+\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+\mathrm{...}+\frac{1}{41}-\frac{1}{45}=-\frac{37}{45}$

$x+\frac{1}{5}-\frac{1}{45}=-\frac{37}{45}$

$x+\frac{8}{45}=-\frac{37}{45}$

$x=-\frac{37}{45}-\frac{8}{45}$