Question

 

Answer 1

2:

a: x/10=-3/5

=>x=-3/5*10=-6

b: =>x=5/14-2/7=5/14-4/14=1/14

c: =>x-2/5=-1/8:5/16=-1/8*16/5=-16/40=-2/5

=>x=0

Answer 2

Bài 5.

A = 1/4 + 1/9 + 1/16 +...+1/2014^2

=1/2^2 + 1/3^2 + 1/4^2 +...+ 1/2014^2 < 1/2.3 + 1/3.4 +....+ 1/2014.2015

Đặt B = 1/2.3 + 1/3.4 +....+ 1/2014.2015

=1/2 -1/3 +1/4 -1/4 +..+1/2014-1/2015

=1/2 - 1/2015 < 1/2 < 3/4

=> A<B<3/4 => A<3/4 (đpcm)