\(\dfrac{1}{7}-\left(\dfrac{5}{21}-x\right)=\dfrac{7}{3}\)
\(\Rightarrow\dfrac{5}{21}-x=\dfrac{1}{7}-\dfrac{7}{3}\)
\(\Rightarrow\dfrac{5}{21}-x=-\dfrac{46}{21}\)
\(\Rightarrow x=\dfrac{5}{21}+\dfrac{46}{21}\)
\(\Rightarrow x=\dfrac{17}{7}\)
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\(5,16-2x=\left(5,7+2,3\right)\cdot\left(-0,3\right)\)
\(\Rightarrow5,16-2x=8\cdot\left(-0,3\right)\)
\(\Rightarrow5,16-2x=-2,4\)
\(\Rightarrow2x=5,16+2,4\)
\(\Rightarrow2x=7,56\)
\(\Rightarrow x=3,78\)
a: =>5/21-x=1/7-7/3=3/21-49/21=-46/21
=>x=5/21+46/21=51/21=17/7
b: =>5,16-2x=8*(-0,3)=-2,4
=>2x=5,16+2,4=7,56
=>x=3,78
