Question

x^4-9x^2<0 (Solve for x)

Answer 1

from -3 to 3 except at x = 0

Answer 2

from -3 to 3.. x=0

Answer 3

\[x^2(x^2-9)=x^2(x-3)(x+3)\]

Answer 4

zeros at -3, 0, and 3

Answer 5

since the term \[x^2\] gives a zero, and it is squared (fancy term is the multiplicity of the 0 is 2) it does not change sign there.

Answer 6

so this thing is positive, then negative, then positive. positive to the left of -3, then negative until 3, then positive after.

Answer 7

you can see from the picture
http://www.wolframalpha.com/input/?i=x^4-9x^2

Answer 8

if you want a fancy answer write
\[(-3,0)\cup (0,3)\]

Answer 9

thanks man. i like that graphing site.