18. Resolva, em H. \( x \) equacion \[ \left|\begin{array}{cccc}-2 & -1 & 0 & 0 \\ 1 & x & -1 & 0 \\ 0 & 0 & 7 & -1 \\ 3 & 0 & 0 & x\end{array}\right|=x^{2}-13 \]

12.3 The equations \( x^{2}+a x+b=0 \) and \( x^{2}+b x+a=0 \) both have real and equal roots. Solve for \( a \) and \( b \), where \( a>0 \) and \( b>0 \).

If \( x-6=0 \) is one of the solutions df the equation \( x+\frac{40}{x}=16 \), determine ONE value of \( y \) for which \( 2 y+3+\frac{40}{2 y+3}=16 \)

17. \( 5 x^{2}+12 x-2=0 \)

If \( x-6=0 \) is one of the solutions of the equation \( x+\frac{40}{x}=16 \), determine ONE value of \( y \) for which \( 2 y+3+\frac{40}{2 y+3}=16 \)

Find the indicated value of the function \( f(x, y, z)=6 x-5 y^{2}+5 z^{3}-7 \). \( f(6,-6,3) \) \( f(6,-6,3)=\square \)