- anonymous

How do I isolate the x in y = 4x - x^2?

- katieb

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- hartnn

why do you need to isolate x from there ?

- anonymous

I need to express the function in terms of y

- IsTim

Maybe it's just really late....but isn't that already "y"?

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- anonymous

...ok i meant in terms of x then whoops

- IsTim

Oh. Ha ha. Made me confused.

- anonymous

basically i need to turn it into a "x=" form instead of "y="

- IsTim

Herrhhh....What grade/course level is this?

- anonymous

I actually need this for a calculus proble, but I'm having a brain fart.

- IsTim

OH..so ln and e^x and all that?

- anonymous

i need to find the radii of the "outer circle" and "inner circle" of the cross section that looks like a donut, so in order to express the radius in terms of the equation, i need it in terms of "x="

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- IsTim

Or do you have to do derivatives too?

- anonymous

I'm using integrals because I need to find the volume of a graph rotated around the y axis

- anonymous

why dont you just complete a square

- IsTim

Wait..does that diagram incldue x,y, z planes, or is that just 2D?

- anonymous

It should be 3D. Okay, the reason why I'm asking this "x isolation" question is because I need to find the volume of the graph of y = 4x - x^2 rotated around the y-axis and bounded by y=0.

- hartnn

completing the square will do it., do you know how to ?

- anonymous

That's the whole problem I'm working on right now.

- anonymous

I tried using the quadrative formula, but I got a numerical answer. Am I using it wrong? I'm having a big brain fart right now T_T

- anonymous

if you ever need to solve a quadratic just complete a square

- anonymous

in this case you need to solve for x, so complete a square to do it o_o

- anonymous

I'm not trying to solve it though. I need to have the x isolated :( Solvng it gives me a numerical answer.

- anonymous

-I feel really stupid right now lol-

- IsTim

Hey, don't say that, or I'll feel stupid for not remembering anything.

- hartnn

let me give you first few steps....
y= 4x-x^2 = -(x^2-4x+4-4)
-y = (x-2)^2-4
now can you isolate 'x' ?

- anonymous

they condition us to grow accustomed to f(x)! f(y) is just as important =[

- anonymous

GOD BLESS YOU HARTNN lol

- anonymous

Thank you everyone, I've got it now :) haha

- hartnn

lol! you too :)

- hartnn

welcome ^_^

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