The maths optional is finite — thirteen years of papers, a knowable set of topics. You don't have to face all of it at once.
Here's the whole rhythm: a few problems a day, picked for you, and you tell us how each one went. That's it — it tunes itself to you as you go. Nothing here grades you.
A missed day isn't a setback. Pick up whenever you're back — we'll be right where you left off.
Check the subjects you've already studied — these are what you're ready to practise. You can change this any time.
Take your time.
This is a real problem — your first one. From tomorrow, a few like it land each day, picked for you. Try it on paper first.
Find the eigenvalues of the matrix
$$A = \begin{pmatrix} 2 & 0 \\ 1 & 3 \end{pmatrix}.$$
Reveal when you're ready — nothing here rushes you.
Solution
The eigenvalues solve $\det(A - \lambda I) = 0$:
$$\det\!\begin{pmatrix} 2-\lambda & 0 \\ 1 & 3-\lambda \end{pmatrix} = (2-\lambda)(3-\lambda) = 0.$$
Because $A$ is lower-triangular, the eigenvalues are just the diagonal entries: $\lambda = 2$ and $\lambda = 3$.