Question

whats an interval, and what is the sign for greater than and less than, i forgot

Answer 1

Greater than: >
Less than: <
An interval represents a range of possible values, so to say, for instance \[1<x<4\]is to say that x is between 1 and 4 (not including 1 or 4). More generically, to say \[a<x<b\]is to say that x is between a and b (not including a or b), where a and b are arbitrary real number constants.