# Adding and Subtracting Matrices – Using Rainbows

This is the most important lesson in the Unit on Matrices! The easiest way to teach adding and subtracting matrices is by color coding.

## Let’s Start Adding and Subtracting Matrices

I start with adding two 2×3 matrices. The reason I do not start with 2×2 matrices is because it is easier to show them that the matrices must be the same size to add or subtract them.
The other reason I use 2×3 matrices is because that means there will be 6 numbers inside each and there are 6 colors to the rainbow (I know that’s debatable but for the sake of the lesson go with it).
RedOrangeYellowGreenBluePurple
Each number from the first matrix gets matched with its Corresponding number in the second matrix. Then they are added or subtracted. I do this with a group activity.
Click Here to Download a Sample Set of Cards for the Activity: Adding and Subtracting Matrices – Using Rainbow Cards
Cards like the ones below are passed out to small groups and they find the solutions. The rest of the activity is available if you are a Algebra 2 Teacher Community Member: Click here to Join Now!
Here are two cards I use to introduce the lesson…
I always start with addition. Simply because it is easier.

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