Final answer:
An example of matrices A and B such that A + B is not invertible, although A and B are invertible.
Step-by-step explanation:
To find an example of matrices A and B such that A + B is not invertible, although A and B are invertible, we can consider the following:
Let A = [1 0] and B = [0 1].
A and B are both invertible because they are non-singular matrices (their determinants are non-zero). However, when we add them together, A + B = [1 0] + [0 1] = [1 1].
The matrix [1 1] is singular because its determinant is zero. Therefore, A + B is not invertible, although A and B are invertible.