Toán Lớp 6: x.20/11=2/1.3+2/5.7+2/7.9+2/9.11

Question

Toán Lớp 6:  x.20/11=2/1.3+2/5.7+2/7.9+2/9.11

catlantuong · Answer

* Đề h&igrave;nh như sai &aacute;, bạn xem lại được ko?   $ dfrac{x.20}{11}$=2/1.3+2/5.7+2/7.9+2/9.11   $ dfrac{x.20}{11}$=2/3 + 2/35 + 2/63 + 2/99   $ dfrac{x.20}{11}$= 2310/3465 + 198/3465 + 110/3465 + 70/3465   $ dfrac{x.20}{11}$= 2688/3465   $ dfrac{x.20}{11}$= 128/165   Ta thấy: 11 = 165: 15   => x.20 = 128 : 15   => x.20 = 8,5 _((3)   => x =  8,5_((3)) : 20   => x = 0,42_((6))   Xin sửa đề: $ dfrac{x.20}{11}$=2/1.3+2/5.7+2/7.9+2/9.11   -> $ dfrac{x.20}{11}$=2/1.3+ 2/3.5 +2/5.7+2/7.9+2/9.11   => $ dfrac{x.20}{11}$= $ dfrac{3-1}{1.3}$ +  $ dfrac{5-3}{3.5}$ +  $ dfrac{7-5}{5.7}$ +  $ dfrac{9-7}{7.9}$ +  $ dfrac{11-9}{9.11}$   => $ dfrac{x.20}{11}$= 1- 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11   => $ dfrac{x.20}{11}$= 1- 1/11   => x . 20/11 = 10/11   => x =  10/11 : 20/11   => x = 10/11 . 11/20   => x = 1/2     $#Dyn.Shun$       $@Shun$~

thanhbinh2k5 · Answer

$ frac{x.20}{11}$ = $ frac{2}{1.3}$ + $ frac{2}{3.5}$ + $ frac{2}{5.7}$ + $ frac{2}{7.9}$ + $ frac{2}{9.11}$ => $ frac{x.20}{11}$ = $ frac{3-1}{1.3}$ + $ frac{5-3}{3.5}$ + $ frac{7-5}{5.7}$ + $ frac{9-7}{7.9}$ + $ frac{11-9}{9.11}$   => $ frac{x.20}{11}$ = 1 - 1/3 + 1/3 -1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11   => (x.20)/11 = 1 - 1/11 => (x.20)/11 = 10/11 => x . 20/11 = 10/11 => x = 10/11 .11/20 = 1/2     Vậy x = 1/2