How to solve 4 by 4 Determinant? | applied electronics engineering

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How to solve 4 by 4 Determinant?

By Applied Electronics - Sunday, November 27, 2016 No Comments
A 4 by 4 determinant of a 4 by 4 matrix can be solved in a similar way to solving 3 by 3 matrix. Consider the following 4 by 4 matrix.

2a + b + c + 3d = 4       ---->(1)
4a - 2b + d = 0         --->(2)
-a + b + 2d = 20     -----(3)
3b + c - d = 13      ---->(4)

where a, b, c and d are variables.

Now the coefficients of the equations can be written in the determinant form D as follows.

Now we can calculate the determinant using either the row as the starting basis,


 or use a column as the basis,


 Let say we use the first row. Then expand the determinant D as follows,



 To understand how this is written see the figure below,



And the sign are alternating.

Then again you can utilize this expansion trick to expand the 3 by 3 matrix as shown below,


Now you can evaluate this equation easily. The answer to this equation is below.


That is the determinant is -16.


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