Volume of a Roof: Find Attic and Surface Area

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Discussion Overview

The discussion revolves around calculating the volume of an attic and the surface area of a roof with a specific geometric configuration. Participants explore the relationship between the dimensions of the attic, the angle of the roof, and the resulting geometric properties, including the roof ridge length.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant describes the attic as having a rectangular base and four plane roof sections, seeking to understand the geometric implications of these features.
  • Another participant suggests that the attic resembles a pyramid with a rectangular base and expresses confusion about the roof ridge's dependence on the angle $\theta$.
  • A later reply clarifies that the attic can be viewed as a triangular prism with half-pyramids at each end, asserting that the length of the roof ridge is independent of the angle $\theta$.
  • Participants discuss the use of trigonometry to find the altitude of the ridge and its relationship to the dimensions of the attic.
  • One participant introduces the concept of a hip roof and suggests visual aids, such as front and side elevations, to better understand the geometry involved.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the geometric configuration and calculations involved. While some agree on the independence of the roof ridge length from the angle $\theta$, others remain confused about the overall visualization and implications of the geometry.

Contextual Notes

Participants mention the need for visual representations to clarify the geometric relationships, indicating potential limitations in understanding without such aids. There are also unresolved aspects regarding the calculations for volume and surface area that depend on further exploration of the geometry.

Poly1
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My house has an attic consisting of a horizontal rectangular base of length $2q$ and breadth $2p$ (where $p < q$) and four plane roof sections each at angle length $\theta$ to the horizontal. Show that the length of the roof ridge is independent of $\theta$ and find the volume of the attic and the surface area of the roof.

I'm struggling with this problem mainly because I can't visualize what's going on. Thanks.
 
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The best I can figure, the attic is in the shape of a pyramid having a rectangular base and two pairs of congruent isosceles triangles as the other sides.

However, if the roof ridge is composed of the lines of intersection between the 4 sections of roof, then this certainly is a function of the angle $\theta$.

So, I am just as confused by this problem as you are.(Drunk)
 
There is a workout for it given in here. I don't understand it though.
 
Okay, now I understand.

The attic is a triangular prism with a half-pyramid (the whole pyramid with square base) at each end.

The roof ridge R is then the length of the prism, which will be the length minus the breadth:

$\displaystyle R=2q-2p=2(q-p)$

This does not depend upon $\displaystyle \theta$ and so is independent of the angle.

Now, using some trigonometry, can you find the altitude of the ridge above the base? We will need this to find the volume of the attic.
 
This is what is called a hip roof, which looks like this:
The ends slope at the same angle as the sides. My advice is to draw a front elevation and a side elevation of this building. That should help you to visualise the geometry of the structure. Denote by $h$ the vertical height of the roof ridge above its base. You should be able to see from the side elevation that $h/p = \tan\theta$. Then use the front elevation to see that $R = 2(q-p)$, as MarkFL says.
 

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