Stage: 3 Challenge Level: 
The outer square has sides of length 1.
Can you work out the area of the inner square and give an explanation of how you did it?
Short problems. Visualising. Circles. Pythagoras' theorem. Generalising. Squares. Area. smartphone. Creating expressions/formulae. Rectangles.
Published April 1997.
Copyright © 2007. University of Cambridge. All rights reserved.
NRICH is part of the family of activities in the Millennium Mathematics Project, which also includes the Plus and Motivate sites.
email: nrich@damtp.cam.ac.uk