The Square Root Of -15 Has Been Described As Useless
The square root of negative fifteen has been described as useless, namely by the mathematician who discovered it. But this number, and other imaginary numbers, aren't totally useless, they're just misunderstood. When this square root was discovered, mathematicians just didn't understand the potential for imaginary numbers. Learn the whole story, and why they aren't useless, in the video below.
The Useless Number
It only seemed useless because it was misunderstood.
An Introduction To Imaginary Numbers
In case you need to freshen up.
from Math Meeting
What Is a Friedman Number?
25 is one of them.