## Solve equation for a roof loading: =[2 x (3/2)Cos(45) x 1] x 2.25

Trigonometric ratios and functions, the unit circle, inverse trig functions, identities, trig graphs, etc.
roofall
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### Solve equation for a roof loading: =[2 x (3/2)Cos(45) x 1] x 2.25

Hi,

=[2 x (3/2)Cos(45) x 1] x 2.25

which is:
4.24x2.25 = 9.54

When I do it, I cant make it work, instead of 9.54 I get 4.77 - what am I doing wrong:

=[2 x (1.5x0.707) x1] x 2.25

which i work as:
= [2 x 1.0605 x1] x 2.25
= 4.77

Any help would be good.

Posts: 136
Joined: Sun Feb 22, 2009 11:12 pm

### Re: Solve equation for a roof loading: =[2 x (3/2)Cos(45) x 1] x 2.25

=[2 x (3/2)Cos(45) x 1] x 2.25
What is the rest of the eqn? Whats on the left side4 of the "="?
which is:
4.24x2.25 = 9.54
Is this maybe just an expression or what you got out of a formula? anyway, the only way to get 4.24 out of the bracketed part is if you don't do the "divided by 2" in the "3/2". Otherwise its wrong & you're right.

roofall
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Joined: Sat Nov 21, 2015 4:02 pm
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### Re: Solve equation for a roof loading: =[2 x (3/2)Cos(45) x 1] x 2.25

Hi, Sorry for the late reply, but here is hopefully all the official info to explain the equation (link to PDF below) - you will see the equation under 'Roof Load', top right of the PDF:

http://postimg.org/image/y5tyi0bsr/

Hope someone can explain. Thanks

buddy
Posts: 197
Joined: Sun Feb 22, 2009 10:05 pm
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### Re: Solve equation for a roof loading: =[2 x (3/2)Cos(45) x 1] x 2.25

So if RL is "Roof Load", W is "width of the bay window's opening in the wall", D is "depth of the bay window, or how far the window sticks out past the rest of the wall", and P is "the pitch angle of the roof, covering the two-floor building, where the bay window is on the first floor", then your eqn is

. . .$RL\, =\, 2.25\, W\, D\, \cos\left(P\right)$

And you're using W = 3, D = 1, P = 45 degrees. Then

. . .$RL\, =\, 2.25\, (3)\, (1)\, \cos\left(45^\circ\right)\, =\, (6.75)\, \left(\dfrac{\sqrt{ 2\,}}{2}\right)\, \approx\, 4.77$

There's lots of fine print on the page of info, saying how this is simplified and is only good for a very specific situation. But I think they made a mistake.