Question

1/1x4 + 1/4x7+....+1/x.(x+3))

Answer 1

= \(\frac{1}{3}\left(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-.....+\frac{1}{x}-\frac{1}{x+1}\right)\) ) 

= \(\frac{1}{3}\left(1-\frac{1}{x+1}\right)\)

=\(\frac{1}{3}x\left(\frac{x+1}{x+1}-\frac{1}{x+1}\right)\)

= \(\frac{1}{3}x\frac{x}{x+1}\)

Answer 2

dè bài la tim x

Answer 3

Tong cua phep. Tinh la 2009/6030