1. WARM-UP 1. Find the distance between the points A(2,-3) and B(4,2)
2. Find an equation for the lower half of the circle centered at C(0,0) with radius 4
3. Find an equation for the line with x-intercept 6 that is parallel to y = 3x +2

2. ANSWERS 1. 2.
3. y = 3x – 18

3. Functions
f(x)=2x-7
g(x)=x+12

4. A function is a special kind of relation.
(A relation is an operation, or series of operations, that maps one number onto another.)

5. In a function, each input value
can give only one
output value.
Does that make sense?
Then try this:

6. If you put a number into a function, you want to know
that only one number can come out.

7. Consider the relation that subtracts 11 from a number:

8. If you put a number in, is there only one possible number that could come out?

9. For any input value, there is only one possible output value.
and have more than one outcome?
Is there any number you can subtract 11 from
So this is a function.

10. The most common way to write this function would be,

11. When we write it like this, x is always the input value,
and y is always the output value,

12. If we wanted to find out what y is when x is 42,
we would substitute 42 for x, and then calculate y.

13. So we could say that 42 belongs to the domain of the function,
and 31 belongs to the range.

14. The domain of a function is the set of all input, or x-, values.
The range of a function is the set of all possible output, or y-, values.

15. One common way to write a function uses function notation.
Function notation looks like this:
Read that, “F of x equals two x plus 1.”

16. Now it becomes obvious that x is the input variable.
You may be asked questions such as,
Given
find f (-2).

17. It’s just a matter of substitution. If you replace every x with –2,
Given
find f(-2).

18. It’s just a matter of substitution. If you replace every x with –2,
you can easily calculate:
Given

19. It’s just a matter of substitution. If you replace every x with –2,
you can easily calculate:
Given

20. Given
find:

21. Functions

22. Functions
A function is a relation in which no two ordered pairs have
the same first coordinate. For every x there is only one y.
(1, 2) (2, 4) (3, 6) (4, 8)
A relation that is a FUNCTION
(1, 2) (2, 4) (2, 5) (3, 6)
A RELATION that is not a function 1 2 3 2 3 4 1 2 3 2 3 4 1 2 3 2 3 4
FUNCTION
FUNCTION
RELATION

23. Functions
Vertical Line Test: If no two points on a graph can
be joined by a vertical line, the
graph is a function.
Function
Relation
Function

24. Functional Notation
An equation that is a function may be expressed
using functional notation. The notation f(x)
(read “f at (x)”) represents the variable y.
E.g., y = 2x + 6 can be written as f(x) = 2x + 6.
Given the equation y = 2x + 6, evaluate when x = 3.
y = 2(3) + 6
y = 12
For the function f(x) = 2x + 6, the notation f(3) means
that the variable x is replaced with the value of 3.
f(x) = 2x + 6
f(3) = 2(3) + 6
f(3) = 12

25. Evaluating a Function
Given f(x) = 4x + 8, find each:
1. f(2)
2. f(a)
f(a) = 4(a) + 8
= 4a + 8
f(2) = 4(2) + 8
= 16
3. f(a + 1)
4. f(-4a)
f(a + 1) = 4(a + 1) + 8
= 4a
= 4a + 12
f(-4a) = 4(-4a) + 8
= -16a+ 8

26. Evaluating a Function
If f(x) = 3x - 1 and g(x) = 5x + 3, find each:
f(2) + g(3)
2. f(4) - g(-2)
= [3(2) -1] + [5(3) + 3] =
= 23
= [3(4) - 1] - [5(-2) + 3]
= (-7)
= 18
f(1) + 2g(2)
= 3[3(1) - 1] + 2[5(2) + 3] =
= 32

27. Evaluating a Function
If g(x) = 2x2 + x - 3, find each:
1. g(2)
g(2) = 2(2) =
= 7
2. g(x + 1)
g(x + 1) = 2(x + 1)2 + (x + 1) - 3
= 2(x2 + 2x + 1) + x
= 2x2 + 4x x - 2
= 2x2 + 5x