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# Finding the Domain of Algebraic Functions

Module by: Pradnya Bhawalkar, Kim Johnston. E-mail the authors

Summary: Finding the domain of various algebraic functions

When finding domain consider the following:

• In rational functions, the denominator cannot equal 0
• When even-degreed roots are in the numerator, the expression under the radical must be greater than or equal to 0
• When even-degreed roots are in the denominator, the expression under the radical must be greater than 0

## Exercise 1

y=12x y 12 x

### Solution

12 12 since 12x0 12 x 0

## Exercise 2

y=x2+9x20 y x 2 9 x 20

### Solution

since there are no even-degreed roots and it is not a rational function

## Exercise 3

y=x2+6x+5 y x 2 6 x 5

### Solution

-5 -1 -5 -1 since x2+6x+50 x 2 6 x 5 0

## Exercise 4

y=x2x+4 y x 2 x 4

### Solution

-4 -4 since x+4>0 x 4 0

## Exercise 5

y=7xx y 7 x x

### Solution

0 0 7 0 0 7 since 7x0 7 x 0 and x0 x 0

## Exercise 6

y=x1x24x y x 1 x 2 4 x

### Solution

0 4 0 4 since x24x>0 x 2 4 x 0

## Exercise 7

y=x21x24 y x 2 1 x 2 4

### Solution

-2 -2 -1 1 2 2 -2 -2 -1 1 2 2 since x210 x 2 1 0 and x240 x 2 4 0

## Exercise 8

y=3x1x+5 y 3 x 1 x 5

### Solution

0 25 25 0 25 25 since x+50 x 5 0 and x0 x 0

## Exercise 9

1|x+1| 1 x 1

### Solution

-1 -1 since x+1>0 x 1 0

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