# Service for Solving Linear Programming Problems

and other interesting typical problems
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## Example №1. Finding the Inverse of a 2x2 Matrix

This solution has been made using the calculator presented on the site.
It is necessary to calculate a matrix A-1, inverse to the given one:
 A = 1 2 1 3
Formula for calculating the inverse matrix:
 A-1 = 1 / det A * A11 A21 A12 A22
A11 ... A22  are numbers (algebraic additions) that will be calculated later.
It is impossible to divide by zero. Therefore, if the determinant of A is zero, then it is impossible to calculate inverse matrix.
Let's calculate the determinant A.
 det A = 1 2 1 3
= 1 * 3 - 2 * 1 = 3 - 2 = 1
Determinant A is not zero. It is possible to calculate inverse matrix.
Let's calculate numbers (algebraic additions)   A11 ... A22
 1 2 1 3
Row number 1
Column number 1
Row 1 and column 1
have been deleted
A11 = ( -1) 1 + 1 * 3 = 3
 1 2 1 3
Row number 1
Column number 2
Row 1 and column 2
have been deleted
A12 = ( -1) 1 + 2 * 1 = -1
 1 2 1 3
Row number 2
Column number 1
Row 2 and column 1
have been deleted
A21 = ( -1) 2 + 1 * 2 = -2
 1 2 1 3
Row number 2
Column number 2
Row 2 and column 2
have been deleted
A22 = ( -1) 2 + 2 * 1 = 1
Result:
 A-1 = 1 / det A * A11 A21 A12 A22
 A-1 = 1 / 1 * 3 -2 -1 1
 A-1 = 3 -2 -1 1
It is necessary to check that   A-1 * A = E.
 3 -2 -1 1
*
 1 2 1 3
=
 b11 b12 b21 b22
b11 = 3 * 1 + ( -2) * 1 = 3 - 2 = 1
 3 -2 -1 1
*
 1 2 1 3
=
 1 b12 b21 b22
b12 = 3 * 2 + ( -2) * 3 = 6 - 6 = 0
 3 -2 -1 1
*
 1 2 1 3
=
 1 0 b21 b22
b21 = -1 * 1 + 1 * 1 = -1 + 1 = 0
 3 -2 -1 1
*
 1 2 1 3
=
 1 0 0 b22
b22 = -1 * 2 + 1 * 3 = -2 + 3 = 1
 3 -2 -1 1
*
 1 2 1 3
=
 1 0 0 1
= E
Thus, the found matrix A-1 is inverse for the given matrix A.

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