The math symbols are very easy to make, although they are not very user-friendly.

Question

Basically, we can type the & sign, immediately followed by a # sign and then the unicode number in decimal (as opposed to hexadecimal), and terminated with a ;.
For example, the not-equal sign's unicode number is 8800, so you can type in
& # 8 8 0 0 ; (without the spaces) to get ≠.

However, the consolation is that there are mnemonics that help us memorize those codes. For example, for the not-equal sign, you can also type in
& n e ; (without the spaces), or & r a d i c ; for √. In this case, the # sign is not required.

For a list of math unicodes, you could try:
http://barzilai.org/math_sym.htm
or there are many others you can find.

Here are some usual mnemonics:
ne ≠
ge ≥
le ≤
radic √
sup2 ²
sup3 ³
sub ⊂
cup ∪
cap ∩
and ∧
or ∨
ang ∠

Greek letters:
alpha α
Alpha Α
etc.

Have fun!