Răspuns:
[tex]$\mathbf{x = \frac{99}{20} }$[/tex]
Explicație pas cu pas:
[tex]$\mathbf{( \frac{3}{14} + \frac{5}{21} x) \div ( - \frac{3}{7} ) = - 3\frac{1}{4} }$[/tex]
[tex]$\mathbf{( \frac{3}{14} + \frac{5}{21} x) \div ( - \frac{3}{7} ) = - \frac{3 \times 4 + 1}{4} }$[/tex]
[tex]$\mathbf{( \frac{3}{14} + \frac{5}{21}x) \times ( - \frac{7}{3} ) = - \frac{12 + 1}{4} }$[/tex]
scapam de paranteze inmultind -7/3 cu fiecare termen din paranteza
[tex]$\mathbf{ - \frac{3}{14} \times \frac{7}{3} - \frac{5}{21}x \times \frac{7}{3} = - \frac{13}{4} }$[/tex]
[tex]$\mathbf{ - \frac{1}{2} - \frac{5}{9} x = - \frac{13}{4} }$[/tex]
[tex]$\mathbf{36 \times ( - \frac{1}{2} - \frac{5}{9} x) = 36 \times ( - \frac{13}{4} )}$[/tex]
[tex]$\mathbf{ - 36 \times \frac{1}{2} - 36 \times \frac{5}{9} x = - 9 \times 13}$[/tex]
[tex]$\mathbf{ - 18 - 20x = - 117}$[/tex]
il mutam pe -18 cu sens schimbat in partea dreapta
[tex]$\mathbf{ - 20x = - 117 + 18}$[/tex]
[tex]$\mathbf{ - 20x = - 99 \Longrightarrow \:\boxed{\mathbf{x = \frac{99}{20} }} }$[/tex]
[tex]\fcolorbox{black}{red}{\textcolor{black}{( - ) × ( - ) = ( + ) \: \:!!! }}[/tex]
Bafta ! :)