Question

no sistema abaixo, qual valor de D, DX e Dy?

{9x - y= 3}
{x + 2y= 9}

D=15 DX=19 DY= 81

D=19 DX= 15 DY= 81

D=19 DX= 15 DY= 78

D=15 DX= 78 DY= 15​

Answer 1

$\boxed{\begin{array}{l}\begin{cases}\sf 9x-y=3\\\sf x+2y=9\end{cases}\\\\\begin{bmatrix}\sf9&\sf-1\\\sf1&\sf2\end{bmatrix}\cdot\begin{bmatrix}\sf x\\\sf y\end{bmatrix}=\begin{bmatrix}\sf3\\\sf9\end{bmatrix}\\\sf D=9\cdot2-(-1)\cdot1=18+1=19\\\begin{bmatrix}\sf3&\sf-1\\\sf9&\sf2\end{bmatrix}\\\sf D_x=3\cdot2-(-1)\cdot9=6+9=15\\\begin{bmatrix}\sf9&\sf3\\\sf1&\sf9\end{bmatrix}\\\sf D_y=9\cdot9-3\cdot1=81-3=78\end{array}}$