Did you solve it? Do you cut cake correctly?

The answer to today's cake puzzles

Earlier today I set you the following three puzzles:

1.You have a square cake, and four friends. How do you divide the cake into five slices of equal size? Each slice must be slice-like, meaning that the knife cuts vertically and the tip of each slice is at the centre of the cake. You have no ruler or tape measure, but you can use the horizontal grid here.