17 – Determine o valor de y para que as Expressões [tex] \begin{gathered} \begin{gathered} \: \overline{ \boxed{\boxed{ \begin{array}{r}\mathsf{ \dfrac{3y}{y \: - \: 4} }\end{array}}}} \end{gathered} \end{gathered} [/tex] e [tex] \begin{gathered} \begin{gathered} \: \overline{ \boxed{\boxed{ \begin{array}{r}\mathsf{3 \: + \: \dfrac{2}{y } }\end{array}}}} \end{gathered} \end{gathered} [/tex] sejam iguais, sabendo que y ≠ 0 e y ≠ 4.
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[tex]\displaystyle \sf \frac{3y}{y-4}=3+\frac{2}{y} \\\\\\ \frac{3y}{y-4}=\frac{3y+2}{y} \\\\\\ 3y\cdot y = (y-4)\cdot (3y+2) \\\\ 3y^2=3y^2+2y-12y-8 \\\\ 3y^2-3y^2-10y- 8 = 0 \\\\ 10 y = -8 \\\\ y = \frac{-8}{10} \\\\\ \huge\boxed{\sf \ y = \frac{-4}{5}\ }\checkmark[/tex]
Após resolver os cálculos, concluímos que o valor de "y" para que as expressões sejam iguais é [tex]\sf y=-\dfrac{4}{5}\,\cdot\\[/tex]
Para resolver esse exercício, basta iguala as expressões, veja:
[tex]\sf\boxed{\sf\dfrac{3y}{y-4}}\quad e\quad\boxed{\sf3+\dfrac{2}{y}}~, com~y\neq0;\,y\neq4[/tex]
[tex] \mathsf{\dfrac{3y}{y-4}=3+\dfrac{2}{y} } [/tex]
[tex] \mathsf{\dfrac{3y}{y-4} -\dfrac{2}{y}=3} [/tex]
[tex] \mathsf{\dfrac{3y^2-2(y-4)}{y(y-4)}=3 } [/tex]
[tex] \mathsf{ \dfrac{ 3y^2 -2y+8}{y(y-4)}=3} [/tex]
[tex] \mathsf{3y^2-2y+8=3y(y-4) } [/tex]
[tex] \mathsf{\diagdown\!\!\!\!\!\!3y^2-2y+8=\diagdown\!\!\!\!\!\!3y^2-12y } [/tex]
[tex] \mathsf{-2y+8=-12y } [/tex]
[tex] \mathsf{ -2y+12y= -8} [/tex]
[tex] \mathsf{ 10y= -8} [/tex]
[tex] \mathsf{ y=-\dfrac{8}{10}} [/tex]
[tex]\boxed{\boxed{\sf y=-\dfrac{4}{5}}}[/tex]
Logo, o valor de "y" para que as expressões sejam iguais é [tex]\sf y=-\dfrac{4}{5}\,\cdot\\[/tex]
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