No space follows a so-called unary operator (one that only attaches to one number).
−1, +4, >7
A space precedes and follows a binary operator (one that joins two numbers).
2 + 3 = 5
3 ≤ x ≤ 10
No space precedes or follows an operator in a subscript or superscript.
xa−5
See the Formatting > Equations section for information on formatting long-form mathematical expressions.