The

**main diagonal**of an x matrix consists of entries whose row number is the same as its column number. In an x matrix, the diagonal is .

Below is a matrix with its diagonal circled.

**trace**of an x matrix is the sum of all the entries on the main diagonal. The trace of a matrix, , is denoted . (Note: In order to calculate the trace of a matrix, the matrix must have the same number of rows and columns. Otherwise, there is no main diagonal.)

Let’s see some examples to better understand.

First example (

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1. Identify the main diagonal

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__Practice__, which has more practice problems and quizzes.

Until next time,

Leah