Question

Answer 1

\(x-\dfrac{20}{11.13}-\dfrac{20}{13.15}-\dfrac{20}{15.17}-...-\dfrac{20}{53.55}=\dfrac{3}{11}\\ x=\dfrac{3}{11}+10\left(\dfrac{2}{11.13}+\dfrac{2}{13.15}+\dfrac{2}{15.17}+...+\dfrac{2}{53.55}\right)\\ x=\dfrac{3}{11}+10\left(\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}+\dfrac{1}{15}-\dfrac{1}{17}+...+\dfrac{1}{53}-\dfrac{1}{55}\right)\\ x=\dfrac{3}{11}+10\left(\dfrac{1}{11}-\dfrac{1}{55}\right)\\x=\dfrac{3}{11}+10.\dfrac{4}{55}\\ x=\dfrac{3}{11}+\dfrac{8}{11}\\ x=1 \)

Answer 2

f, x - 20/11.13 - ... - 20/53.55 = 3/11

   x - 10(1/11 - ... - 1/55) = 3/11

   x - 10(1/11 - 1/55) = 3/11

   x - 10.4/55 = 3/11

   x - 40/55 = 3/11

   x             = 3/11 + 40/55

   x             = 1

             Vậy x = 1