# Find the domain of the expression.

• Sep 1st 2010, 07:56 PM
DHS1
Find the domain of the expression.
Can you help me find the domain of these expressions?

1.) -x^4+x^3+9x

2.) 2r^2-5/3r+6

3.) 1/sqrt(x-1)
• Sep 1st 2010, 08:05 PM
undefined
Quote:

Originally Posted by DHS1
Can you help me find the domain of these expressions?

1.) -x^4+x^3+9x

2.) 2r^2-5/3r+6

3.) 1/sqrt(x-1)

Does 5/3r mean 5/(3r) or (5/3)r?

For domain questions such as these, remember: division by zero is undefined, and square root of a negative number is not in reals.
• Sep 1st 2010, 08:22 PM
DHS1
Quote:

Originally Posted by undefined
Does 5/3r mean 5/(3r) or (5/3)r?

For domain questions such as these, remember: division by zero is undefined, and square root of a negative number is not in reals.

Thank you. However I do know what you just said, I just can't figure those three problems out. And I meant (2r^2-5)/(3r+6)
• Sep 1st 2010, 08:29 PM
undefined
Quote:

Originally Posted by DHS1
Thank you. However I do know what you just said, I just can't figure those three problems out. And I meant (2r^2-5)/(3r+6)

1) All reals
2) Solve the inequality $3r+6 \ne 0$
3) Solve the inequality x - 1 > 0