`(3x)/(2.5)+(3x)/(5.8)+(3x)/(8.11)+(3x)/(11.14)=1/21`
`=>x(3(2.5)+3/(5.8)+3/(8.11)+3/(11.14))=1/21`
`=>x(1/2-1/5+1/5-1/8+1/8-1/11-1/14)=1/21`
`=>x*(1/2-1/14)=1/21`
`=>x*3/7=1/21`
`=>x=1/21:3/7=1/9`
Vậy `x=1/9`
3 x /2.5 + 3 x /5.8 + 3 x /8.11 + 3 x/11.14 = 1/21
⇒x (3 ( 2.5 ) + 3/5.8 + 3/8.11 + 3/11.14 ) = 1/21
⇒x (1/2 − 1/5 + 1/5 − 18 + 18 − 1/11 − 1/14 ) = 1/21
⇒x⋅ ( 1/2 − 1/14 ) = 1/21
⇒x ⋅ 3/7=1/21
⇒x . 3/7= 1/21
⇒x=1/21:3/7=1/9
Vậy x=1/9
\(\dfrac{3x}{2.5}+\dfrac{3x}{5.8}+\dfrac{3x}{8.11}+\dfrac{3x}{11.14}=\dfrac{1}{21}\)
\(x.\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+\dfrac{3}{8.11}+\dfrac{3}{11.14}\right)=\dfrac{1}{21}\)
\(x.\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)
\(x.\left(\dfrac{1}{2}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)
\(x.\dfrac{3}{7}=\dfrac{1}{21}\)
\(x=\dfrac{1}{21}:\dfrac{3}{7}\)
\(x=\dfrac{1}{9}\)