**Coordinate systems: **

They are two mutually perpendicular coordinate lines which intersect in the origin O on each line.

**The four quadrants in a coordinate system:**

Quadrant I is the area where a>0 and b>0.

Quadrant II is the area where a<0 and b>0.

Quadrant III is the area where a<0 and b<0.

Quadrant IV is the area where a>0 and b<0.

**Distance: **

The distance between any two points is defined as:

.

**Data sets:**

The grouping or collection of similar or related data.

**Subsets:**

If A and B are sets and every element of A is also an element of B, then: A is a subset of B, denoted by.

**Product of two data sets:**

If S and T are sets, the product set of S and T will be denoted by , which satisfies

.

**Line:**

A geometric figure formed by a point moving along a fixed direction and the reverse direction.

**Slope of a line:**

If and are arbitrary two points on the line, the slope can be calculated by

.

**Midpoint of any two points:**

The distance between two arbitrary points is given by

.