Spend your weekend doing O'level geometry 'cos you don't trust what's written in a book you're reading (John Michell's "The View Over Atlantis" page 115 of the 3rd ed. Ballantine Books 1973 ISBN 345-02881-3-150, in case you're interested).
This book and many others claim that the angle of slope of the Great Pyramid of Khufu (noted as 51° 51') is contained within a particular construction based on the vesica piscis figure.
Actually, the vesica piscis construction results in an angle of 51° 36' 38".
So either the pyramid builders didn't base the pyramid on this construction, or they weren't completely accurate, or the remains of the pyramid are so eroded we can't be sure what the intended angle of slope might have been.
Any way up, you can't say that this construction gives you a 51° 51' angle, 'cos it doesn't.
See the attachment for the proof.