Gilbert Strang and MIT OpenCourseWare (OCW) often provide selected solutions for free. This is the most "authentic" source and usually includes corrections for any errata found in the print version.

To appreciate the value of the solution manual, let’s look at what you will actually solve in each chapter of the 4th edition.

If your answer differs from the manual, do not assume you are wrong or the manual is wrong. There are often multiple correct representations (different bases for the same subspace). Use the manual to understand if your approach is equivalent.

Finding a reliable by Gilbert Strang is often the turning point for students struggling with the complexities of vector spaces, eigenvalues, and linear transformations.