Trying to remember maths after 40 years

**KRe** · April 30th 2012, 10:02 AM

I have forgotten some/ most / all of my maths knowledge.
I am trying to solve

x=10-x² *t
for x with respect to t.

I know that I used to be able to do this and I also know that I thought it was simple but my memory has gone and who keeps text books for 40 years.
Thanks for any help

**Prove It** · April 30th 2012, 10:15 AM

Originally Posted by KRe

I have forgotten some/ most / all of my maths knowledge.
I am trying to solve

x=10-x² *t
for x with respect to t.

I know that I used to be able to do this and I also know that I thought it was simple but my memory has gone and who keeps text books for 40 years.
Thanks for any help

$\displaystyle \begin{align*} x &= 10 - t\,x^2 \\ t\,x^2 + x &= 10 \\ x^2 + \frac{1}{t}\,x &= \frac{10}{t} \\ x^2 + \frac{1}{t}\,x + \left(\frac{1}{2t}\right)^2 &= \frac{10}{t} + \left(\frac{1}{2t}\right)^2 \\ \left(x + \frac{1}{2t}\right)^2 &= \frac{40t}{4t^2} + \frac{1}{4t^2} \\ \left(x + \frac{1}{2t}\right)^2 &= \frac{40t + 1}{4t^2} \\ x + \frac{1}{2t} &= \pm \frac{\sqrt{40t + 1}}{2t} \\ x &= -\frac{1}{2t} \pm \frac{\sqrt{40t+1}}{2t} \\ x = \frac{-1 - \sqrt{40t + 1}}{2t} \textrm{ or } x &= \frac{-1 + \sqrt{40t + 1}}{2t} \end{align*}$

**BillSimpson** · April 30th 2012, 10:25 AM

If you knew algebra once and you want to bring the memory back then look for a copy of "Forgotten Algebra." It is an inexpensive paperback written for exactly this purpose and is available used or in libraries. Do every problem in the book as fast as you can go and then do them all over again. You should find your memory coming back after that.

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