Let A be a 2x2 matrix:
A = \begin{bmatrix} a & b \\ c & d \end{bmatrix}
The determinant of A is given by:
det(A) = ad - bc
For A to be invertible, its determinant must be non-zero:
ad - bc \neq 0
Now, we are given that a = 7 and d = c. So, we can substitute
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