# Math Help - Quadratic Equations and Substituting "Appropriately?"

1. ## Quadratic Equations and Substituting "Appropriately?"

I have a section in my book that is asking me to "make an appropriate substitution" for a set of problems; and the book doesn't even give examples on how to do this sort of thing.

Here is one for example:

x^4-5x^2+4=0

Help, anyone?

Thanks

2. ## Re: Quadratic Equations and Substituting "Appropriately?"

Let $x^2=k$

3. ## Re: Quadratic Equations and Substituting "Appropriately?"

Originally Posted by annon25
I have a section in my book that is asking me to "make an appropriate substitution" for a set of problems; and the book doesn't even give examples on how to do this sort of thing.

Here is one for example:

x^4-5x^2+4=0

Help, anyone?

Thanks
They want you to make a substitution (let's use "k", as Quacky suggests) so that your equation can be written as
ak^2 + bk + c = 0.

With k = x^2, we have
k^2 - 5k + 4 = 0
(k .... )(k ....) = 0
etc.