View Full Version : How I find the Domain definition
pop000
Dec 11, 2010, 07:47 AM
I need to find the Domain definition of this Function:1/x^4-3x^3+9x^2-7
thanks.
galactus
Dec 11, 2010, 10:06 AM
You have written:
\frac{1}{x^{4}}-3x^{3}+9x^{2}-7.
I assume you mean:
\frac{1}{x^{4}-3x^{3}+9x^{2}-7}
This is why grouping symbols are important.
pop000
Dec 11, 2010, 11:10 AM
Yes this what I mean so how I find the Domain definition?
Thanks
galactus
Dec 11, 2010, 11:21 AM
Which one? You did not say. I assume that latter? Does find the 'Domain definition' mean find the domain?
If so:
Factor the denominator. Set the factors equal to 0 and solve for x.
These are the values NOT in the domain because they result in division
by 0.
This particular quartic has 2 real and 2 complex roots. I assume you are
not dealing with the complex so find the two real roots.
Graph it and you can see the vertical asymptotes. That is where there is
division by 0 and not in the domain.
pop000
Dec 12, 2010, 01:46 AM
I mean the second Equation but is not 7 is need to be 7x
galactus
Dec 12, 2010, 01:58 AM
Is this correct?:
\frac{1}{x^{4}-3x^{3}+9x^{2}-7x}
If so, factor:
\frac{1}{x(x-1)(x^{2}-2x+7)}
Set each factor to 0. x=0 is one solution, x=1 is another.
The remaining quadratic has complex roots.
The values x=0 and x=1 are NOT in the domain because they give division by 0.
pop000
Dec 12, 2010, 07:44 AM
Thank you for helping now I understand:)