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We have a 2 by 2 matrix on the left hand side. We are applying the determinant to it because of the vertical bars.
The determinant of
is
This only works for 2 by 2 matrices.
We compute the product of the diagonals, then subtract those products.
In the case of
the determinant is
Set this equal to the 35 and solve for x.
or
or
We see that the solution set consists of nonreal complex numbers of the form a+bi, where
If your teacher has not covered imaginary numbers or complex numbers just yet, then the answer would be "no real solutions".
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