# 3: Operations on Matrices


In the previous chapter we learned about matrix arithmetic: adding, subtracting, and multiplying matrices, finding inverses, and multiplying by scalars. In this chapter we learn about some operations that we perform on matrices. We can think of them as functions: you input a matrix, and you get something back. One of these operations, the transpose, will return another matrix. With the other operations, the trace and the determinant, we input matrices and get numbers in return, an idea that is different than what we have seen before.

• 3.1: The Matrix Transpose
The transpose of a matrix is an operator that flips a matrix over its diagonal. Transposing a matrix essentially switches the row and column indices of the matrix.
• 3.2: The Matrix Trace
In this section we learn about a new operation called the trace. It is a different type of operation than the transpose. Given a matrix A , we can “find the trace of A ,” which is not a matrix but rather a number. We formally define it here.
• 3.3: The Determinant
In this chapter so far we’ve learned about the transpose (an operation on a matrix that returns another matrix) and the trace (an operation on a square matrix that returns a number). In this section we’ll learn another operation on square matrices that returns a number, called the determinant. We give a pseudo-definition of the determinant here.
• 3.4: Properties of the Determinant
In the previous section we learned how to compute the determinant. In this section we learn some of the properties of the determinant, and this will allow us to compute determinants more easily. In the next section we will see one application of determinants.
• 3.5: Cramer's Rule
This section shows one application of the determinant: solving systems of linear equations. We introduce this idea in terms of a theorem, then we will practice.

Thumbnail: Schematic diagram for the Rule of Sarrus for computing a 3x3 determinant (CC BY-SA 4.0 International; Eisenbahn%s via Wikipedia)

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