Alegra
posted by Alissa .
solve the inequality express in interval notation
x^4 + 4x^3  9x^2  36x < 0

Algebra 
Writeacher
Assistance needed.

Alegra 
Alissa
Ah yeah which is why I post the question.

Alegra 
Ms. Sue
Alissa  Writeacher corrected your spelling of "Algebra" so that a math expert would see your post.
Jiskha doesn't have any experts in Alegra (whatever that is). 
Alegra 
Steve
x^4 + 4x^3  9x^2  36x
= x(x^3 + 4x^2  9x  36)
Cubics are hard to solve, so look for easy roots. They will be factors of 36.
A little synthetic division reveals
(x+4)(x+3)x(x3)
Now since everything is single roots, the graph alternates between positive and negative between roots.
Since it's a quartic with a positive coefficient, it will be positive before the lowest root and after the highest root.
So,
y > 0 for x < 4
y < 0 for 4 < x < 3
y > 0 for 3 < x < 0
y < 0 for 0 < x < 3
y > 0 for x > 3 
Alegra 
Alissa
Thank you I appreciate your help and the fact that you didn't make a big issue out of a typo. Again thank you.
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