ALGEBRAIC FUNCTIONS (Easy to see.)

A set of all X's is called the DOMAIN

A set of all Y's is called the RANGE

A FUNCTION is when the X value of each X,Y pair of coordinates is always a different value.

A sample set of XY pairs of a function      { (5,2) (6,4) (7,8) }
A sample set of XY pairs "Not" a function { (5,2) (5,4) (5,8) } f(x) = y or in this case f(x) = 2x + 1 since y = 2x + 1
f(DOMAIN independent value) = (RANGE dependent value)

 In this example the range y = 2x + 1 This is a function, so... f(x) = 2x + 1 EXAMPLE 1 when x = - 1: EXAMPLE 2 when x = + 2: Given;  f(x) = 2x + 1   When;  x = -1  then;    f(-1) = 2(-1) + 1 so;         f(-1) = - 2 + 1 and;      f(-1) = -1 conclusion;  f(x) = -1 when x = -1 Given;  f(x) = 2x + 1 when;  x = 2 then;   f(2) = 2(2) + 1 so;        f(2) = 4 + 1 and;     f(2) = 5 conclusion;  f(x) = 5 when x = 2

Also see.....
Equation manipulation of a straight line

Domain and Range Explained
http://www.studycoach.com/alg/classnotes/functions/domain&range.html
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