Draw a number line and mark all described points on it. Numbers that are either positive or less than −3.

A number line is a one dimensional graph (rather an endless straight line) on which one can represent every possible real number. Usually we have zero serving as the center of the number line, with the right hand side serving as the positive part of the real line and the left hand side as the negative part of the real line.

A number line is endless which implies there is no bound to a number line.

Any number on the real line is denoted by a dark spot on the real line. For example if one needs to denote 3 on the real line he/she has to mark 3 with a spot.

There are three kind of intervals that can be represented on the number line namely closed [ ] , open ( ) and semi-closed or semi- open [ ) or ( ]. Intervals on number line are being shown by thickening that part of the real line that are under consideration.

For example: (4 , 5) is representing by thickening the number line between 4 and 5 with open ends , i.e. circles on digit 4 and 5.

[4 , 6] is represented by thickening the number line between 4 and 6 with closed or black dot ends.

Similarly semi open and semi closed intervals are represented by thickening the interval between those two points with appropriate circles and dots on the endpoints.

According to the given question we need to mark all described points that are positive. Thus all points greater than zero are to be thickened (excluding zero). This is done by having an open end on point zero and thickening the whole of the right hand side or the positive side of the number line.

Similarly to represent all described points on the number line less than ( -3) (excluding ( - 3)) can be done by having an open end on point ( - 3) and thickening the whole of the negative side to the left of ( - 3).

Thus to represent all the required points we can write them in a set A as:

A = { x : x > 0; x < ( - 3) }.