# I Surface integral

1. Jul 7, 2016

### chetzread

in part b , we can find mass by density x area ?
is it because of the thin plate, so, the thickness of plate can be ignored?

2. Jul 7, 2016

### BvU

There is no ignoring the thickness going on. The density function is a function of only two variables (*), so it provides mass/area, not mass/volume.

(*) as pointed out with the z=f(x,y) callout

3. Jul 7, 2016

### chetzread

so, z=f(x,y) provide info that density depends on 2 variables only????

4. Jul 7, 2016

### BvU

Yes $$\rho(x,y,z) = \rho(x,y,3-x-y) = \rho(x,y)$$it is multiplied with something of dimension length2 so $\rho$ has the dimension mass/area

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