Any maths buffs?

I have a question that is puzzling me...

Show that the expression

                f(x,y)= x^2−2xy+2(y^2)−6y+3

has a stationary point at (x,y) = (3,3). What type of stationary point is it?

so for the derivative i get

dy/dx=2x/(2x-4y+6) which would give an infinite gradient (dy/dx=6/0) therefore not being a stationary point?

thanks for any help.

sorry if i missed something.

isn't there a maths geek thread?

PM fruitbat, he may know.

don't you need to find the second derivative to find the nature of a turning point?
you presume the first derivative = 0 otherwise it wouldn't be stationary...

PM Onelesscardigan, he can help.

i read the title as "Any muff baths?"

Srsly.

(sorry i can't help with the maths bit).

don't you need to find the second derivative to find the nature of a turning point?
you presume the first derivative = 0 otherwise it wouldn't be stationary...

yeah, but the first derivative doesn't give zero, it gives infinity, and it should give zero, otherwise it's not a stationary point?

You don't want dy/dx you are finding a stationary point on a surface so you need to find the point at which the function has zero derivative w.r.t x and w.r.t y.

So take the partial derivative of f(x,y) w.r.t x and the partial derivative w.r.t y

f(x,y)=x^2−2xy+2(y^2)−6y+3

\frac{\partial f}{\partial x}= 2x-2y
= 2(x-y)
\frac{\partial f}{\partial y}=-2x+4y-6
=2(x+2y-3)

What is this saying?

Eq 1 is telling us the rate of change f w.r.t x and eq w.r.t y. We wish both of these to be zero hence it a pair of simultaneous equations.

so .. now you tell me the rest.

My brain is weeping blood.

My brain is weeping boredom

Well you should have joined me in the pub at six then, doofus.

Didnt get invited mate.

That's because I looked in my phones address book and did not have your number- and whose fault is that?

You never asked

:(

Don't ruin the best thread on the forum.

they're having a problem with numbers too, though.

badtmy wins.

they're having a problem with numbers too, though.

:)

they're having a problem with numbers too, though.

Accountancy = numbers

Maths = patterns and relationships.

http://www.ucl.ac.uk/Mathematics/geomath/level2/pdiff/pd9.html seems to be what you need.

Googling 'partial derriviative', 'hessian matrix', or 'saddle point' may also help.

Accountancy = numbers

Maths = patterns and relationships involving numbers.

fixed.

Dammit is trying solve a problem, to derive Balki's numbers. Their relationship depends on the solution.

:) sorry i'll stop being a smart-arse.

I hope this thread goes on and on. I just can't resist peering at big brains on display.

Object, paging Object.