Where'd I go wrong?

[Spectre927]

Eq. = 8x^-4 - 17x^-2 + 2. I u-subbed for x^-2

8u^2 - 17u +2

(8u-1)(u-2) u= 1/8 u = 2

x^-2 = 1/8= 64
x^-2 = 2 = 1/4
When I enter them into the equation it doesn't work.

(17^2) - 4(8)(2)= 225

Thanks

 

[stapel]

Eq. = 8x^-4 - 17x^-2 + 2. I u-subbed for x^-2

Why? What are you trying to do? (No instructions were included in your post.)

And what is 8x^-4 - 17x^-2 + 2 equal to? (You have an "equals" sign at the beginning, but I don't know what "Eq." stands for.)

Thank you.

Eliz.

 

[pka]

\(\displaystyle \L
\begin{array}{l}
x^{ - 2} = \frac{1}{8}\quad \Rightarrow \quad x = \pm \sqrt 8 \\
x^{ - 2} = \frac{1}{2}\quad \Rightarrow \quad x = \pm \sqrt 2 \\
\end{array}\)

 

[Denis]

x^-2 = 1/8= 64

NO!
1 / x^2 = 1 / 8 ; x^2 = 8 ; x = 2sqrt(2)
Other one similarly wrong.

 

[Denis]

Having a bad day, pka :shock:
Your 2nd one is now incorrect...right?

 

[Spectre927]

Sorry. It was equal to 0. I was trying to find all the real roots. Eq. was equation.

 

[Spectre927]

I see. I plugged U into the X rather than solve for X. Thanks...