# Thread: Domain of Functions

1. ## Domain of Functions

Find the domain of f(x) = -3x^2 + 5x.

How is this done algebraically?

2. ## Re: Domain of Functions

The given function has no even radicals or potential for division by zero, or anything else which would cause output to be undefined, so its domain is all reals.

3. ## Re: Domain of Functions

Originally Posted by harpazo
Find the domain of f(x) = -3x^2 + 5x.
How is this done algebraically?
It cannot done algebraically whatever that is.
One must understand the concepts involved.
But again you seem very reluctant to try that approach.

4. ## Re: Domain of Functions

Originally Posted by MarkFL
The given function has no even radicals or potential for division by zero, or anything else which would cause output to be undefined, so its domain is all reals.
Is there a difference between an even and odd radical?

5. ## Re: Domain of Functions

Originally Posted by harpazo
Is there a difference between an even and odd radical?
Yes, an odd radical, such as a cube or fifth root, can have a negative radicand, where as an even radical like a square or fourth root cannot, when we are talking about real number function values.

6. ## Re: Domain of Functions

Originally Posted by MarkFL
Yes, an odd radical, such as a cube or fifth root, can have a negative radicand, where as an even radical like a square or fourth root cannot, when we are talking about real number function values.
Good. What about if we are talking about complex number function values? Am I stepping into an area considered advanced algebra?

7. ## Re: Domain of Functions

Originally Posted by harpazo
Good. What about if we are talking about complex number function values? Am I stepping into an area considered advanced algebra?
The real number field is ordered. In it we can have upper & lower bounds.
The complex number field is not ordered (cannot be ordered in the same sense).
In the complex number field functions still have domains. However the word "range" suggest order, therefore we tend to use image instead.

Good notes.