[tex]\large\boxed{\begin{array}{l}\sf (\bf {ESCCAI})\sf A\,soluc_{\!\!,}\tilde ao\,do\,sistema\\\begin{cases}\sf x+y=9\\\sf \ell og_2x+\ell og_2y=3\end{cases}~\sf\acute e:\\\sf a) (4,5),(5,4 )~~d)(0,9),( 9,0)\\\sf b)(1,8),(8,1)~~e)(10,-1),(-1,10)\\\sf c)(3,6),(6,3)\end{array}}[/tex]
[tex]\large\boxed{\begin{array}{l}\underline{\sf soluc_{\!\!,}\tilde ao\!:}\\\begin{cases}\rm x+y=9\\\rm\ell og_2x+\ell og_2y=3\end{cases}\\\rm \ell og_2x+\ell og_2y=3\\\rm \ell og_2(x\cdot y)=3\longrightarrow x\cdot y=2^3\\\rm x\cdot y=8\\\begin{cases}\rm x+y=9\\\rm x\cdot y=8\end{cases}\\\\\begin{cases}\rm y=9-x\\\rm x\cdot y=8\end{cases}\end{array}}[/tex]
[tex]\large\boxed{\begin{array}{l}\rm x\cdot (9-x)=8\\\rm 9x-x^2=8\\\rm x^2-9x+8=0\\\rm\Delta=b^2-4ac\\\rm\Delta=(-9)^2-4\cdot1\cdot8\\\rm\Delta=81-32\\\rm\Delta=49\\\rm x=\dfrac{-b\pm\sqrt{\Delta}}{2a}\\\\\rm x=\dfrac{-(-9)\pm\sqrt{49}}{2}\\\\\rm x=\dfrac{9\pm7}{2}\begin{cases}\rm x_1=\dfrac{9+7}{2}=\dfrac{16}{2}=8\\\\\rm x_2=\dfrac{9-7}{2}=\dfrac{2}{2}=1\end{cases}\end{array}}[/tex]
[tex]\large\boxed{\begin{array}{l}\rm se\,x=8:\\\rm y=9-x\\\rm y=9-8\\\rm y=1\\\rm se\,x=1:\\\rm y=9-x\\\rm y=9-1\\\rm y=8\\\rm S=\{(1,8),(8,1)\}\\\huge\boxed{\boxed{\boxed{\boxed{\rm\dagger\red{\maltese}~\blue{alternativa~b}}}}}\end{array}}[/tex]
