Question

1.Cho A=1/1.2+1/3.4+...+1/99.100

C/m :7/12<A<5/6

2.Tim x:

a.2/(x+2)(x+4)+4/(x+4)(x+8)+6/(x+8)(x+14)

b.x-10/30+x-14/43+x-5/95+x-148/8=0

Lam giup minh nhe 

Minh dang can gap

Answer 1

Answer 2

1/               1/1.2 +1/3.4 =7/12 
1/5.6+...1/99.100 >0 suy ra A> 7/12 (1) 
A =1/2 +1/3-1/4+1/5-1/6+.....1/99-1/100=5/6-(1/... 
Từ(1) và (2) suy ra: 7/12<A<5/6