Question

tìm x biết : \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+.....+\frac{1}{x\left(x+1\right)}=\frac{17}{18}\)

 

Answer 1

=> 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ........ + 1 /x - 1/x + 1 = 17 /18

=> 1 - 1/x+1 = 17/18

=> 1/x+1 = 1/18

=> x + 1 = 18

=> x = 17 (tm)

Vậy x = 17 nha!

Ai mk mk lại !!

Answer 2

1/1.2 + 1/2.3 + 1/3.4 +......+ 1/x(x+1) = 17/18

=> 1- 1/x+1 = 17/18

=>  1/x +1 = 1-17/18

=> 1/x+1 = 1/18

=> x= 17 

Answer 3

ta có: 1/1.2+1/2.3+1/3.4+1/4.5+...+1/x(x+1)=17/18

 1-1/2+1/2-1/3+1/3+1/4+1/4-1/5+...+1/x-1/x+1=17/18

 1-1/x+1=17/18

 1/x+1=1-17/18

 1/x+1=1/18

suy ra: x+1=18

x=18-1

x=17

Answer 4

x=17

De ma!Kien thuc lop 5 day.