Practical guide and verification
An inverse may not exist
A square matrix has an inverse only when it is nonsingular. If the determinant is zero, or the rows/columns are linearly dependent, there is no ordinary inverse to compute.
Near-singular matrices
A matrix can be technically invertible yet numerically ill-conditioned. Small changes in the inputs may then produce large changes in the inverse, so a long decimal output can look more trustworthy than the data justify.
Common mistake
Do not use matrix inversion as an automatic replacement for solving a linear system. Numerical methods that solve Ax=b directly are often more stable and efficient than explicitly forming A⁻¹.