# Math Help - finding (x,y)

1. ## finding (x,y)

I'm trying to help a friend w/ calc but it's been a long time since i've done it. it's on partial derivatives. Any help is 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) 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?

2. Originally Posted by buckaroobill
I'm trying to help a friend w/ calc but it's been a long time since i've done it. it's on partial derivatives. Any help is 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) 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?
For fixed height the rate of change of surface area is:

D_w S(w,h) = (15.63)*(0.425)w^(0.425-1) * (h^.0725) sq in/pound

where D_w denotes the partial differential with respect to w.

RonL