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quackensack

Member

Registered: 2007-02-27

Posts: 47

partial derivatives problem

Not really sure how this is done so any help would be appreciated.

The function S(w, h) = (15.63w^0.425) * (h^.0725) gives the approximate surface area (in sq. inches) of a person h inches tall who weighs w pounds.

1) A boy grows taller while maintaining a weight of 130 pounds. At what rate is his surface area increasing when he's 5'4" tall?

2) Now at his full height of 5'9", he goes to the gym and bulks up. At what rate is his body surface increasing when he reaches 140 pounds?

Stanley_Marsh

Member

Registered: 2006-12-13

Posts: 345

Re: partial derivatives problem

1) His weight remain constant , you can see w as a constant then find the derivative

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Numbers are the essence of the Universe

quackensack

Member

Registered: 2007-02-27

Posts: 47

Re: partial derivatives problem

Sorry, I'm confused about how to do that.

Stanley_Marsh

Member

Registered: 2006-12-13

Posts: 345

Re: partial derivatives problem

it's just my opinion , if you see w as a constant , then  the derivative will be

where w equal to 130

Last edited by Stanley_Marsh (2007-03-15 15:36:07)

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Numbers are the essence of the Universe

quackensack

Member

Registered: 2007-02-27

Posts: 47

Re: partial derivatives problem

would it just be h^0.725 * 6.64 * w^-.575 ?

(for w/ respect to w)

Last edited by quackensack (2007-03-15 15:55:42)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: partial derivatives problem

That's right, assuming that you made a typo in your first post and the formula is meant to involve h^0.725.

So then you could use that formula to do question 2).

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It wanted to be normal.