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# Maths question...help needed. PROBLEM SOLVED!

Y = 4xz – x^4 – z^4

(Squiggly d’s btw)

Dy/dx = 4z – 4x^3

Dy/dz = 4x – 4z^3

D2y/dx2 = -12x^2

D2y/dz2= -12z^2

How can I work out d2y/dxdz or d2y/dzdx which is the same thing….?

21 Comments

tree fiddy

Original Poster

splatsplatsplat

tree fiddy

mazel tov

what is z?
a constant or a function z(x) that consists of x?

edit: i think z may be a function of x and y, z(x,y)? otherwise d2y/dxdy = 0?
Edited by: "mug51" 19th May 2011

do your own homework!

Original Poster

Rupz

do your own homework!

not homework, just doing this for fun oO

Original Poster

mug51

what is z?a constant or a function z(x) that consists of x?edit: i think … what is z?a constant or a function z(x) that consists of x?edit: i think z may be a function of x and y, z(x,y)? otherwise d2y/dxdy = 0?

Partial differentiation question.

Y(X,Z) = 4xz – x^4 – z^4

davidbeckham187

not homework, just doing this for fun oO

ok, let you off......geek

Do you mean d^2y/dxdz instead of d^2y/dxdy?

davidbeckham187

not homework, just doing this for fun oO

oO......you do head wrecking math for fun ?!?!

Original Poster

CamoChris

Do you mean d^2y/dxdz instead of d^2y/dxdy?

yes....lol

Original Poster

CamoChris

Do you mean d^2y/dxdz instead of d^2y/dxdy?

is it 4 or -12?

davidbeckham187

is it 4 or -12?

4, as d^2y/dxdz is d(dy/dx)/dz i.e dy/dx differentiated w.r.t z

flip a coin, heads is 4 tails is -12....

its -12 as i got tails

Original Poster

CamoChris

4, as d^2y/dxdz is d(dy/dx)/dz i.e dy/dx differentiated w.r.t z

oh alright. Thanks....!

I have (4xz + 16xz^3 - 16x^4 - 16z^4)/d^2y =dxdz

Then rearranging i get (d^2y)^2/above = your equation, just squared...

So the answer I get finally, is the square root of the answer in bold at the top

Doesn't x = y = z = 0 solve all of those equations?

Try standing on your head

Mr Weasle

Try standing on your head

Too hard. Can I stand on yours instead?

To geek it up a little further, that's a smooth function on RxR and so d^2y/dxdz and d^2y/dzdx are the same.

Original Poster

jenovat

To geek it up a little further, that's a smooth function on RxR and so … To geek it up a little further, that's a smooth function on RxR and so d^2y/dxdz and d^2y/dzdx are the same.

ha ha lol.
stop looking at my threads!

Original Poster

looking back now i feel like an idiot for posting this thread.
these are tooo easy now.
ha ha!
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