@WM-R  
It’s sometimes used in physics and engineering. For instance, electrical engineering uses imaginary units in circuit analysis. Although otherwise it’s not really generally useful in most day-to-day situations.

@Chicago Ted
 
@Background Pony #96DC
 
@mathprofbrony
 
Thanks for the explanation. I cannot even begin to imagine how the heck you’re going to convince kids they’ll need that kind of knowledge after leaving school.
 
@mathprofbrony
 
Your name is irably well-suited.

@mathprofbrony  
Square root of -1. Hey, I was right!

I hear the call of my cutie mark!
 
@Background Pony #96DC  

 
To be precise:
 
i is the square root of -1. That is, the equation x^2 = -1 has solutions x=i and x=-i.
 
A number is real if it is one of the usual numbers: 3, -12, pi, -14.5, sqrt(2), etc.
 
A number is purely imaginary if it is c i for some real number c. So 3i, -12i, pi i, -14.5i, (sqrt(2))i etc., are all purely imaginary.
 
A number is complex if it has both a real and an imaginary part: numbers of the form a + bi are complex.
 
Of the roots of -1, there is one real root, -1 itself, which is its own first root (as anything is its own first root); two purely imaginary roots, i and -i, which are its square (2nd) roots; and all the rest of its roots, whether even or odd, are complex, of the form a+bi, with a = cos(2pi* k/n) and b = sin(2pi* k/n) for some rational number k/n. For instance, the cube (third) roots of -1 are
 
cos(2pi1/6) + sin(2pi1/6) i, and
 
cos(2pi5/6) + sin(2pi5/6) i.
 
Note that any root of -1 is also a root of 1, by doubling the power: a cube root of -1 is a sixth root of 1. You can think of all of these roots as points on the circle of radius 1 around the origin; if you’re a rational fraction of the way around (that’s 2pi radians) from the point (1,0), then you’re at some root of 1, and if your fraction of 2pi radians has an even denominator in lowest , you’re at a root of -1.

@WM-R  
An imaginary number is an even root (square, 4th, 6th root, etc.) of a negative number, represented by the symbol i, i.e. 3i = imaginary 3.

@WM-R @Mildgyth  
Something to do with the square root of -1, if I recall correctly from my junior math class back in high school.

@WM-R
 
Not even i anymore.

@ShadowSlut
 
To be fair, you could argue the same of almost any subject. English essays just get longer, for example.
 
Though I can relate. I was terrible at Maths because I could never get the formulas down, and trying to force it through repetition just made me resentful. Much later when I was idly trying to figure it out myself, suddenly things clicked.
 
@Mildgyth
 
I have no idea what most of those things you list mean. What the frag is an imaginary number?

@Background Pony #2572  

 
*asocial. Anti-social is much different.

Anti-social forever. 🙂