# Nonlinear inequality

• February 1st 2009, 07:56 PM
tmac11522
Nonlinear inequality
Solve the nonlinear inequality. Express the solution using interval notation and graph the solution set. http://www.webassign.net/www27/latex...fc5b763b5b.gif

I am stuck on where the line should start, I know it is a positive infinity, it appears as if it starts at -1, but its not correct.
• February 1st 2009, 08:08 PM
TKHunny
Start by reasoning on the Domain and Range.

Domain doesn't help much.

Range?

$x^{4} \ge 0$

$x^{9}$ has the same sign as x.

This restricts your solutions to $x > 0$.

After that:

$x^{9} - x^{4} > 0$

$x^{4} \cdot (x^{5} - 1) > 0$

Only $x \ne 0$ for $x^{4}$. How about the other piece?

$x^{5} - 1 = (x-1)(x^{4}+x^{3}+x^{2}+x+1)$

That big piece restricts nothing, being always greater than zero (0).

The only piece of any remaining significance is (x - 1).

This is a great problem to see if you were paying attention in class. Were you?
• February 1st 2009, 08:13 PM
Edit: sorry, didnt see tkhunny's post. Feel free to ignore this
$x^9>x^4$
if $x \not = 0$
$\frac{x^9}{x^4} >1$
$x^5>1$
$(x^5)^{1/5} >1^{1/5}$
$x>1$

if x = 0 then $0^9\not > 0^4$

Quote:

I know it is a positive infinity,
Right
• February 1st 2009, 08:22 PM
Krizalid
Well it's like having $x^3>1$ then the cubic root "does the work," since this is just $x>1.$ But this is actually the answer, but it does require a little bit of justification.