Even though it ought to be impossible, the square of the number i is minus one. That formula led us to create complex numbers, which led to complex analysis, one of the most powerful areas of mathematics. With the help of complex numbers, mathematicians improved methods to calculate trigonometric tables, found more powerful methods to understand waves, heat, electricity, and magnetism, and the mathematical basis of quantum mechanics.
Becca Hirsbrunner photographed this fabulously constructed Z proportions letter. Interestingly, every element but the diagonal bar can be rationalized.