`(2/(11.13)+2/(13.15)+....+2/(19.21)).462-[0,04/(x+1,05):0,12=19`
`=>(1/11-1/13+1/13-1/15+....+1/19-1/21).462-(2/(50(x+1,05)).25/3=19`
`=>(1/11-1/21).462-1/(3(x+1,05))=19`
`=>10/231. 462-1/(3x+3,15)=19`
`=>20-1/(3x+3,15)=19
`=>1/(3x+3,15)=1`
`=>3x+3,15=1`
`=>3x=-2,15`
`=>x=-43/60`
Vậy `x=-43/60`
Giải:
\(\left(\dfrac{2}{11.13}+\dfrac{2}{13.15}+...+\dfrac{2}{19.21}\right).462-\left[\dfrac{0,04}{x+1,05}:0,12\right]=19\)
\(\left(\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}+...+\dfrac{1}{19}-\dfrac{1}{21}\right).462-\left[\dfrac{1}{\dfrac{25}{x+\dfrac{21}{20}}}:\dfrac{3}{25}\right]=19\)
\(\left(\dfrac{1}{11}-\dfrac{1}{21}\right).462-\left[\dfrac{1}{25.\left(x+\dfrac{21}{20}\right)}:\dfrac{3}{25}\right]=19\)
\(20-\left[\dfrac{25.1}{3.25.\left(x+\dfrac{21}{20}\right)}\right]=19\)
\(\dfrac{1}{3.\left(x+\dfrac{21}{20}\right)}=20-19\)
\(\dfrac{1}{3.x+\dfrac{63}{20}}=1\)
\(1:\left(3.x+\dfrac{63}{20}\right)=1\)
\(3.x+\dfrac{63}{20}=1:1\)
\(3.x+\dfrac{63}{20}=1\)
\(3.x=1-\dfrac{63}{20}\)
\(3.x=\dfrac{-43}{20}\)
\(x=\dfrac{-43}{20}:3\)
\(x=\dfrac{-43}{60}\)