To add or subtract matrices, they must have the same dimensions. When adding, corresponding entries are added, while when subtracting, negatives are subtracted correctly. Algebraic expressions within matrices can also be added or subtracted provided the matrices have matching dimensions, otherwise the result is undefined.

1. Adding and Subtracting Matrices

2. To add matrices, they must have the same dimensions.
Add the corresponding entries. (The ones with the same color.)
2 + 5
3 + -1
3 + 5
-6 + 5

3. The result is a new matrix with the same dimensions, and the entries added.

4. When subtracting, be careful to subtract negatives correctly!
-1 – (-6) = 5
3 – (-1) = 4
-3 – (-6) = 3
-6 – 4 = -10

5. Algebraic expressions can also be added and subtracted in a matrix.

6. If the dimensions do not match, the result is undefined.