1. **Problem Statement:** Calculate the size of the marked angles in problem 2a, which is a square divided by two diagonals forming four angles labeled $\alpha$, $b$, $e$, and $d$. 2. **Recall properties of a square and its diagonals:** - All angles in a square are $90^\circ$. - The diagonals of a square are equal in length and bisect each other at right angles ($90^\circ$). - The diagonals divide the square into four right-angled isosceles triangles. 3. **Using the properties:** - Since the diagonals intersect at right angles, the angles formed at the intersection are all $90^\circ$. - Each of the four angles $\alpha$, $b$, $e$, and $d$ at the intersection point is therefore $90^\circ$. 4. **Final answer:** $$\alpha = b = e = d = 90^\circ$$ This completes the calculation for problem 2a.