1. The problem statement, all variables and given/known data Find the mass of the surface of the triangle with vertices (2,0,0), (0,2,0) and (0,0,1) if the density is 4xz. The solution is attached as TheSolution.jpg. 2. Relevant equations Integration. Cross product. Plane equation: a(x-x_0) + b(y-y_0) + c(z-z_0) = 0 where <a,b,c> = n (vector that is normal to the plane) and where (x_0,y_0,z_0) is any arbitrarily chosen vertice. 3. The attempt at a solution Having watched (1) and read (2),: (1) (2) http://www.math.oregonstate.edu/hom...usQuestStudyGuides/vcalc/surfint/surfint.html I have successfully reached the dS = sqrt(3/2) dA step and for the next step, I'm supposed to multiply the density by the surface area in order to get the mass of the surface but, I just don't see how I'm supposed to get the (4x – 2x^2 – 2xy) part nor do I see how the variable density, 4xz, relates to that; I'm not sure that it should relate but I feel it should. Could someone please help me understand the step I am stuck on? Any help would be greatly appreciated! Thanks in advance!