Calculating the Area of a Plane in the First Octant

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Homework Help Overview

The discussion revolves around calculating the area of a plane in the first octant defined by the equation ax + by + cz = d, where a, b, c, and d are positive real numbers. The original poster seeks to show that the area can be expressed as [d² sqrt(a² + b² + c²)] / 2abc.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the lack of direct formulas for the area of planes and consider using surface integrals. One participant suggests breaking the plane into simpler shapes to find the area and questions how to determine the boundaries of the shape. Another participant identifies the area as a triangle and proposes using the cross product to find the area of a parallelogram, then halving it for the triangle area. They express difficulty in simplifying their results to match the expected form.

Discussion Status

The discussion is active, with participants exploring various methods to approach the problem. One participant has indicated a resolution to their earlier confusion, suggesting that some progress has been made, though the overall consensus on the best approach has not been reached.

Contextual Notes

Participants are working under the assumption that the area is finite and are considering the geometric properties of the plane in relation to the axes that bound it. There is mention of a potential careless mistake affecting calculations, indicating the complexity of the problem.

quietrain
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Homework Statement


consider the area of a plane in first octant where a,b,c,d are positive real numbers
show that the area is [d2 sqrt(a2+b2+c2)] / 2abc

Homework Equations


ax+by+cz = d

The Attempt at a Solution



ok i tried to search for formulas for areas of planes but there seem to be none !
i found one at paula's calculus notes that is about using surface integrals but it seems not for this problem?

can anyone point me to the right direction? thanks!
 
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quietrain said:

Homework Statement


consider the area of a plane in first octant where a,b,c,d are positive real numbers
show that the area is [d2 sqrt(a2+b2+c2)] / 2abc

Homework Equations


ax+by+cz = d

The Attempt at a Solution



ok i tried to search for formulas for areas of planes but there seem to be none !
i found one at paula's calculus notes that is about using surface integrals but it seems not for this problem?

can anyone point me to the right direction? thanks!

Hey there.

I'm going to assume that the area is finite.

Since planes are linear objects you can break them up into simple shapes and then add up the areas.

First you need to find the boundary of the shape. Have you got any ideas how to do that?

(Hint think of the axis that bound the plane!)
 
i realize that it is a triangle?

can i use the cross product to get area of parallelogram and then half it to get the triangle area?

i got 3 coordinates for the 3 places of intercept

namely
0,0,c -------- for x=0, y=0, z=c
0,d/b,0
d/a,0,0

i calculated out but somehow i get a very complicated solution. and i can't get it to fit into the elegant form in the first post ><

i even use half base x height by using projection to get height and then using base, but the expression is horrible too...

anywhere i did wrong?
 
oH i solved it... it was a careless mistake ><... thanks!
 

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