Math Is Fun Forum

lolanicolle

Guest

please help

Δ?ƒ/Δ?x and Δ?ƒ/Δ?y. ƒ(x,y) = xy² + x²y

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: please help

Do you want the partial derivatives of that function? If so, then you just treat it as a normal derivation problem but act as if all variables are constants, except the one that you're differentiating with respect to.

So, d[xy² + x²y]/dx is the same as d[ax + bx²]/dx, where a and b are the constants y² and y respectively, and that is equal to a + 2bx, which is y² + 2xy.

Differentiate with respect to y in a similar manner.

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Why did the vector cross the road?
It wanted to be normal.

lolanicolle

Guest

Re: please help

Thank you for your response, i was looking at that problem for a while.

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: please help

I'm rusty, but this might be a mistake:

Doesn't the constant go to zero, and the 2y is the answer for 2nd deriv?

Last edited by John E. Franklin (2007-12-08 15:29:53)

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igloo myrtilles fourmis

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: please help

Nice catch! You're quite right.

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Why did the vector cross the road?
It wanted to be normal.