Question

[Trần Tiến Quang]

Tính c/a1 a2 + c/ a2 a3 +.     + c/ an-1 a                  biết a2- a1=.    = an - an-1= k

Answer 1

[Lưu Quang Trường]

\(\dfrac{c}{a_1a_2}+\dfrac{c}{a_2a_3}+...+\dfrac{c}{a_na_{n+1}}\)

=\(\dfrac{c}{a_1}-\dfrac{c}{a_2}+\dfrac{c}{a_2}-\dfrac{c}{a_3}+.....+\dfrac{c}{a_n}-\dfrac{c}{a_{n+1}}\)

=\(\dfrac{c}{a_1}-\dfrac{c}{a_{n+1}}\)