Help me calculate length when i know angles?

woodoo

Can someone help me to calculate the the length of 2 sides of a triangle when i know the angles and one of the lengths.

Say the triangle in link below is 35 degrees at angle B, Angle A and C are 72.5 degrees and i know the length of the bottom of the triangle is 4 meters. What are the other 2 lengths. http://www.mathplanet.com/education/pre-algebra/introducing-geometry/triangles

I put this in AH because of the traffic it gets. If it gets shut down can someone please PM me the answer as i need those lengths urgently to calculate how much wood i need for a job tomorrow.

Aspiring

Sine rule? Length of side divided by the sin of its opposite angle is equal to length of another side over the sin of its opposite angle.

https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcSvUlYK6HBOGJYyxWAED9TWNHVxcF6ef6dC9SYPj3PA1F21bijftLGxm66S

woodoo

Aspiring wrote: »

Sine rule? Length of side divided by the sin of its opposite angle is equal to length of another side over the sin of its opposite angle.

https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcSvUlYK6HBOGJYyxWAED9TWNHVxcF6ef6dC9SYPj3PA1F21bijftLGxm66S

Thanks aspiring i realize i am in mathematics forum now i thought it was AH for higher traffic. I have no clue how to use sine rules.

Aspiring

I only have the calculator on my phone but I worked it out as 6.651m for each length. You can probably type "sine rule calculator" into google and you just fill in what you have and it'll tell you the answer.

woodoo

Aspiring wrote: »

I only have the calculator on my phone but I worked it out as 6.651m for each length. You can probably type "sine rule calculator" and you just fill in what you have and it'll tell you the answer.

That sounds too long. Picture a gable end of a roof. And the building is 4 meters wide. I am trying to calculate the length of the side of the roof.

http://www.premierbydesign.co.uk/hip-to-gable.htm

Aspiring

woodoo wrote: »

That sounds too long. Picture a gable end of a roof. And the building is 4 meters wide. I am trying to calculate the length of the side of the roof.

http://www.premierbydesign.co.uk/hip-to-gable.htm

The diagonal? It would be 6.651 if all angles and sides given are correct. Google agrees.

Academia

So your triangle is an isosceles (as two angles are equal) triangle. Length AB = BC = x and AC = 4 m

1. Sine Rule. x/sin 72.5 = 4/sin 35 => x = 6.67 m approx.

2. Cosine Rule. 4^2 = x^2 + x^2 - 2x^2 cos 35 => x = 6.67 m approx.

You could look formulae up.

gctest50

woodoo wrote: »

That sounds too long. Picture a gable end of a roof. And the building is 4 meters wide. I am trying to calculate the length of the side of the roof.

http://www.premierbydesign.co.uk/hip-to-gable.htm

http://www.calculator.net/triangle-calculator.html?vc=35&vx=&vy=&va=&vz=4&vb=72.5&angleunits=d&x=91&y=10

woodoo

Thanks guys for your help.

mickdw

woodoo wrote: »

Thanks guys for your help.

At such a high pitch, the rafter length is going to be far longer than the width of the gable.
Are you sure about the 72 degrees. That would be a very very steep roof.

Academia

It's actually 6.651 m.

If you don't wan to use sine or cosine rule, draw a line from point B to bisect AC (let's say at D). Now you can cut out a right angled triangle. AD = 2 m, Angle B now halved = 17.5 degrees.

SOHCAHTOA. Sine = opp/hyp

2/x = sin 17.5 degrees

bnt

I was going to say something like Academia there. Because it's an isosceles triangle, you can divide it in two to give you two identical right-angled triangles. Then it's standard trigonometry for the rest.

Ciaran

You could just draw a scale model of the triangle and measure the sides. Might be the quickest way.

e.r

Wouldn't fancy getting my roof done by you !!

woodoo

e.r wrote: »

Wouldn't fancy getting my roof done by you !!

Ha, Ha i'm not a roofer, i was just doing the buying. And i have since learned the my angles where all wrong. But the formula given here were good to calculate the correct lengths in the end so thanks to all who helped.

e.r

Sorry for been smart:-)