Saying that "2+2=5" is not mathematically crazy. It is just an invitation to broaden your mind and discover some beautiful mathematics that you are not (yet) familiar with: group theory, topology, and Euler identity. 1/n

2+2=5 is true in the group (R/Z,+). In that context, 0=1. Picture it as a circle. Going around the circle once takes you back to the same point. Going around the circle 2,3,4 or 5 times gives the same result. This is surpringly useful in math/physics/tech. 2/n

In topology, a circle can be defined as a line segment (such as the real numbers between 0 and 1) in which the two end points (0 and 1) are identified. If you do basic arithmetics under that assumption, you will see that 2+2=5 is perfectly fine. 3/n

From the point of view of the trigonometric circle, 0=1 or 2+2=5, can be explained using the identity exp(2 π i)=1. More generally,, The multiplicative group of complex numbers of module 1 is useful in trigonometry, in electromagnetism, and even in quantum mechanics. 4/n, n=4.