Triangle QRS is isosceles and right-angled.
Beatrix reflects the P-shape in the side QR to get an image.
She reflects the first image in the side QS to get a second image.
Finally, she reflects the second image in the side RS to get a third image.
What does the third image look like?
If you liked this problem, here is an NRICH task
that challenges you to use similar mathematical ideas.
This problem is taken from the UKMT Mathematical Challenges.