-Imaginary numbers aren't only used in mathematics, but they can also be used in engineering.
-When using imaginary numbers in engineering, we don't use the unit "i." We use the unit "j" so as not to confuse imaginary numbers with the unit for electric currents, which is also "i." [source]
Imaginary numbers in engineering. [source]
-Nowadays, imaginary numbers are almost always referred to as complex numbers. One of its definitions is that it is a complex number with no part that is real. These are called "purely imaginary numbers." [source]
-0 is considered both a real number AND an imaginary number.
-Imaginary numbers can also be identified as complex numbers, where the part that is real is 0.
-When looking at cartesian complex plane or graph, the horizontal axis is the "real number axis" and the vertical axis is the "imaginary number axis."
A Venn Diagram of sets of all numbers. [source]
A complex number plane. [source]
-The square root of -1 MUST be considered either without meaning or as an expression with two possible values (i or -i). [source]
-Imaginary numbers weren’t always thought of as useful or relevant to everyday mathematical problems. Though, it was later discovered that they could be used to create things like complex numbers.