Question

Tính :

10/56+10/140+10/260+...+10/1400

Answer 1

Tách ra rồi tính như bt Minh nhek

Answer 2

= 5/28+5/70+5/130+...+5/700

=5/3.(3/4.7+3/7.10+3/10.13+...+3/25.28)

=5/3.(1/4-1/7+1/7-1/10+1/10-1/13+...+1/25-1/28)

=5/3.(1/4-1/28)=5/3.3/14=5/14

k mik nha