8.2 Relations, Graphs and symmetry
1) A relation is a set of ordered pairs of numbers. Relations are usually written in the
set builder notation.
For example {(x, y) | y £ x}, { (x, y) | y = x2 + 1 } etc.
In most cases we just write y £ x, y = x2 + 1 etc.
Many a times we just give the list of ordered pairs { (1,2) , (3,5), (-2,6) }
A relation can be best understood by sketching its graph.
First, we will study graphic equations on the coordinate plane.
To graph an equation on the co-ordinate plane, find the solutions by giving a value to one variable and this will help solve the other variable. Then graph the solutions.
Example Find the distance of the point A(3,4) from 0 [origin].
Solution : A (x1, y1) = ( 3, 4 )
Distance of A from the origin 0, is
Example Find the distance between the points (2,3) and (7,8)
Solution : Let A (x1, y1) = (2, 3) and B (x2 , y2) = (7, 8)
Distance between points A and B, is.
Example The distance between the point A (8,8) and a point B on the y - axis is 10.
Find the Coordinates of B.
Solution : Since point B is on the y-axis, B is (0, y2)
Let A (x1, y1) = (8, 8)
The distance between A and B, is
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