Beans Posted April 27, 2011 Share Posted April 27, 2011 My exam is on Monday. Spherical and cylindrical coordinates are my 2nd least favorite part of this class, behind 3D surfaces.I love ES math threads. Good luck. Do lots of practice problems ("harder" ones), and you'll destroy that freaking test! Link to comment Share on other sites More sharing options...
SonOfWashington Posted April 27, 2011 Share Posted April 27, 2011 Good luck. Do lots of practice problems ("harder" ones), and you'll destroy that freaking test! It's eight questions and a third of the final grade. Super nervous. Link to comment Share on other sites More sharing options...
bcl05 Posted April 27, 2011 Share Posted April 27, 2011 But, what if the walls aren't straight vertical? It could be that the walls are trapezoidal, so that the roof and floor are rectangles of different size, like a pyramid with the top cut off.... Link to comment Share on other sites More sharing options...
Chiefinonhaze Posted April 27, 2011 Author Share Posted April 27, 2011 This is a HW review for the exam. I learned this at the beginning of Calc 3, but I can't get this question right. It seems like you guys are posting different answers. What is the consensus right answer? ' Link to comment Share on other sites More sharing options...
SonOfWashington Posted April 27, 2011 Share Posted April 27, 2011 But, what if the walls aren't straight vertical? It could be that the walls are trapezoidal, so that the roof and floor are rectangles of different size, like a pyramid with the top cut off....I feel it would have specified. Link to comment Share on other sites More sharing options...
Beans Posted April 27, 2011 Share Posted April 27, 2011 It's eight questions and a third of the final grade. Super nervous. Don't be. The more practice, the less nervousness. Trust me, I've been there. Then again, it depends on how harsh your Prof is. Some are generous with the partial credit and what not, some will mark the whole problem wrong if you accidentally leave off a negative sign. Hell, I even had a persnickety ass prof that would take off points for grammatical errors in proofs (he was the head of the department). Link to comment Share on other sites More sharing options...
Larry Posted April 27, 2011 Share Posted April 27, 2011 Haven't read the other posts yet. The roof and floor both have an area of XY, so cost of (roof+floor) is 26xy. The area of the walls is (perimeter*height) = (2x+2y)z. So the cost of the walls is 10(2x+2y)z Final formula, cost = 26xy + 10(2x+2y)z Link to comment Share on other sites More sharing options...
Weganator Posted April 27, 2011 Share Posted April 27, 2011 But, what if the walls aren't straight vertical? It could be that the walls are trapezoidal, so that the roof and floor are rectangles of different size, like a pyramid with the top cut off.... Back... and just in time for a good one.. Let t = angle between the floor and the not 90 degree wall. Let L = the hypotenuse each triangle formed for each wall Let K = the base of the triangle formed for each wall (the amount of length that is being reduce from each side from floor to ceiling due to angle) z / L = sin(t) -> L = z / sin(t) z / K = tan(t) -> K = z / tan(t) Area of floor: 12 * x * y area of Wall x: 2 * 10 * x * L area of Wall y: 2 * 10 * y * L area of ceiling: 14 * (x - K) * (y - K) C(x,y,z,t) = 12xy + 20xz/sin(t) + 20yz/sin(t) + 14 * (xy - xz/tan(t) - yz/tan(t) + (z/tan(t))^2) Not nearly as confident on that one.. but i think thats it Note: This assumes that the 'trapezoidal pyramid angles' are the same... if they differed, you would need differing values of L and K for each angle Link to comment Share on other sites More sharing options...
Dr. Do Itch Big Posted April 27, 2011 Share Posted April 27, 2011 Lot of upper high level math yay! Sow have you guys done jacobian yet? I swear my calc 3 teacher made our classes life a lot more difficult than he should have. Link to comment Share on other sites More sharing options...
Capt. Kaos Posted April 27, 2011 Share Posted April 27, 2011 This is WAY outta my league but my wife gave me this answer: 20yz + 20xz + 26xy = C Link to comment Share on other sites More sharing options...
dfitzo53 Posted April 27, 2011 Share Posted April 27, 2011 Haven't read the other posts yet. The roof and floor both have an area of XY, so cost of (roof+floor) is 26xy. The area of the walls is (perimeter*height) = (2x+2y)z. So the cost of the walls is 10(2x+2y)z Final formula, cost = 26xy + 10(2x+2y)z This is the same as the other formulas posted. They're all just expressed slightly different ways. They're all correct. (I'm pretty sure you know this Larry, I'm just trying to reassure the OP.) Link to comment Share on other sites More sharing options...
SonOfWashington Posted April 27, 2011 Share Posted April 27, 2011 Lot of upper high level math yay! Sow have you guys done jacobian yet? I swear my calc 3 teacher made our classes life a lot more difficult than he should have.I don't remember the term being used, but looking at Wikipedia's article for Jacobian, some of the content looks familiar. Link to comment Share on other sites More sharing options...
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