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Artist 52 [7]
3 years ago
9

-x=-y+2 and 3y+4=2x solve using matrices

Mathematics
1 answer:
MissTica3 years ago
8 0

\begin{cases}-x=-y+2\\3y+4=2x\end{cases}\implies\begin{cases}x-y=-2\\2x-3y=4\end{cases}

In matrix form, this is

\begin{bmatrix}1&-1\\2&-3\end{bmatrix}\begin{bmatrix}x\\y\end{bmatrix}=\begin{bmatrix}-2\\4\end{bmatrix}

The coefficient matrix has determinant

\begin{vmatrix}1&-1\\2&-3\end{vmatrix}=-3+2=-1\neq0

so it has an inverse, which is

\begin{bmatrix}1&-1\\2&-3\end{bmatrix}^{-1}=\begin{bmatrix}3&-1\\2&-1\end{bmatrix}

Multiply both sides by the inverse matrix:

\begin{bmatrix}3&-1\\2&-1\end{bmatrix}\begin{bmatrix}1&-1\\2&-3\end{bmatrix}\begin{bmatrix}x\\y\end{bmatrix}=\begin{bmatrix}3&-1\\2&-1\end{bmatrix}\begin{bmatrix}-2\\4\end{bmatrix}

\implies\begin{bmatrix}x\\y\end{bmatrix}=\begin{bmatrix}-10\\-8\end{bmatrix}

so that x=-10 and y=-8.

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