# what is the domain of this function

• Jun 10th 2009, 01:33 PM
emmalou264
what is the domain of this function
can anyone help tell me what the domain of this function is please

f(x) = 1
_________

sqr root of (1-x)(7+x)
• Jun 10th 2009, 01:40 PM
VonNemo19
Quote:

Originally Posted by emmalou264
can anyone help tell me what the domain of this function is please

f(x) = 1
_________

sqr root of (1-x)(7+x)

What makes f(x) undefined. ie What make the denominator 0, or what makes the radical undefined (negative)

The domain is all values of x for which the function is defined.

I'll give u one place that it's not defined.........

x<-7

here's another

x>1

here's another

x=1

here's another

x=-7

So are you familiar with interval notation?

\$\displaystyle (-7,1)\$
• Jun 10th 2009, 03:28 PM
mr fantastic
Quote:

Originally Posted by VonNemo19
What makes f(x) undefined. ie What make the denominator 0, or what makes the radical undefined (negative)

The domain is all values of x for which the function is defined.

I'll give u one place that it's not defined.........

x<-7

here's another

x>1

here's another

x=1

here's another

x=-7

So are you familiar with interval notation?

\$\displaystyle [-7,1]\$

A square bracket means that the endpoint is included. A round bracket means that the endpoint is not included. So a slight correction to this answer is required: (-7, 1).

@OP: Since \$\displaystyle (1 - x)(7 + x) > 0\$ is required, the interval is most easily found by drawing a graph of the parabola \$\displaystyle y = (1 - x)(7 + x)\$ and looking for the values of x such that y > 0.
• Jun 10th 2009, 03:56 PM
VonNemo19
Quote:

Originally Posted by mr fantastic
A square bracket means that the endpoint is included. A round bracket means that the endpoint is not included. So a slight correction to this answer is required: (-7, 1).

@OP: Since \$\displaystyle (1 - x)(7 + x) > 0\$ is required, the interval is most easily found by drawing a graph of the parabola \$\displaystyle y = (1 - x)(7 + x)\$ and looking for the values of x such that y > 0.

I simply cannot believe I did that. aaaaaaarrrrrrrrrrrrrrrrrgggggggggghhhhhhhhh!!!!!!! !!!!!!!