An (Ordered Pair) is denoted by (a, b), where 'a' represents the first projection (x-coordinate) and 'b' represents the second projection (y-coordinate). Unlike standard sets where order is irrelevant {a, b} = {b, a}, in ordered pairs order is critical: (a, b) != (b, a) unless a = b. Two ordered pairs are equal if and only if their corresponding projections are identical: [(x, y) = (a, b) <=> x = a and y = b]. This fundamental property allows us to formulate and solve simultaneous algebraic equations.
Quick Concept Check
Question: What is the equality condition for two ordered pairs? If (x - 1, 11) = (8, y + 3), find x and y.
Key Answer: (x, y) = (a, b) <=> x = a and y = b. Here x - 1 = 8 => x = 9, and y + 3 = 11 => y = 8.
The Cartesian Product of two non-empty sets X and Y, denoted as [X x Y], is the set of all ordered pairs whose first projection belongs to X and second projection belongs to Y: [X x Y = {(x, y) : x in X and y in Y}]. The number of elements in the Cartesian product equals the product of their individual cardinalities: [n(X x Y) = n(X) * n(Y)]. Note that in general [X x Y != Y x X], although their cardinalities are always equal: [n(X x Y) = n(Y x X)]. Furthermore, the Cartesian product of any set with the empty set is empty [X x empty = empty].
Quick Concept Check
Question: What is the formula for n(X x Y)? If n(X) = 3 and n(Y) = 5, find n(X x Y).
Key Answer: n(X x Y) = n(X) * n(Y). Here n(X x Y) = 3 * 5 = 15.
A Cartesian product can be illustrated using two primary visual methods:
1. (Arrow Diagram): Set X is drawn as a vertical column of elements and Set Y as an adjacent column; an arrow is drawn from each element in X to every element in Y.
2. (Cartesian / Graphical Diagram): Set X is laid horizontally as the x-axis and Set Y vertically as the y-axis; the elements of X x Y appear as intersection points on a coordinate grid.
Quick Concept Check
Question: What are the two standard visual diagrams used to represent a Cartesian product?
Key Answer: The Arrow Diagram and the Cartesian (Graphical/Grid) Diagram.
The Cartesian plane (R x R or R^2) is divided by two perpendicular axes (the x-axis X X' and y-axis Y Y') intersecting at the Origin (0, 0) into four distinct quadrants:
• Quadrant I: x > 0 and y > 0 (+, +).
• Quadrant II: x < 0 and y > 0 (-, +).
• Quadrant III: x < 0 and y < 0 (-, -).
• Quadrant IV: x > 0 and y < 0 (+, -).
Crucial rules: Any point lying on the x-axis has a y-coordinate of zero (x, 0). Any point lying on the y-axis has an x-coordinate of zero (0, y).
Quick Concept Check
Question: Identify the quadrant of (-2, -3). What coordinate is zero for a point lying on the y-axis?
Key Answer: (-2, -3) lies in Quadrant III (-, -). For any point on the y-axis, the x-coordinate is 0.