x - $\dfrac{10}{11.13}$-$\dfrac{10}{13.15}$-$\dfrac{10}{15.17}$-$\dfrac{10}{17.19}$-...-$\dfrac{10}{53.55}$=$\dfrac{3}{11}$
Giải
Ta có: x - $\dfrac{10}{11.13}$-$\dfrac{10}{13.15}$-$\dfrac{10}{15.17}$-$\dfrac{10}{17.19}$-...-$\dfrac{10}{53.55}$
= x-10( $\dfrac{1}{11.13}$-$\dfrac{1}{13.15}$-$\dfrac{1}{15.17}$-$\dfrac{1}{17.19}$-...-$\dfrac{1}{53.55}$)
= x-10( $\dfrac{1}{11}$-$\dfrac{1}{13}$-$\dfrac{1}{13}$-$\dfrac{1}{15}$-...-$\dfrac{1}{53}$-$\dfrac{1}{55}$)
= x-10( $\dfrac{1}{11}$-$\dfrac{1}{55}$)
=x-10$\dfrac{4}{55}$
=x-$\dfrac{8}{11}$
\Rightarrow x-$\dfrac{8}{11}$ =$\dfrac{3}{11}$
x=$\dfrac{3}{11}$+$\dfrac{8}{11}$
x=1
Vậy x=1
Đáp số: x=1