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Surface area!


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Hi all,

A quick queestion on trigonometry, as there is no specific section I thought I would try my luck here!

How do you work out the surface area of a Triangle if you have all the dimensions and angles involved?

Probably very easy for those who know but I spent, much to my regret, most of my maths lessons scratching my navel.



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To make a complete fool of myself and embarrass my self beyond recovery:

Area of a triangle is half of the base multiplied by the height.

Easy if the triangle is right angled.  If it does not have any right angles then you have to use trig to find the height.  Construct a right angles triangle by extending the "base" and then right angle up to the 3rd point (i.e. the one not lying on your "base").  This line up from the projected base to the 3rd point is the height.  You know one side (the hypotenuse) - as it is one side of your actual triangle, plus you know all the angles so you the trig:

    Sine(angle)=Opposite side/Hypotenuse


    Cosine(angle)=Adjacent side/Hypotenuse



(Now I will go and hide in a corner with shame at having forgotten so much school maths and having got the above all wrong (so please do correct my ignorance).

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Surley, it makes no difference whether the triangle is acute, obtuse whatever?

I think you are confusing the issue slightly, Ian with determining the height of a triangle if you know the size of the base and angles etc.

If you know all the sizes of any irregular figure (polygon etc.) you can work out the area: and, of course the angles, usually by dividing the figure into convenient triangles, squares etc as proportion.

Use this!

It's easier!


Maths behind it here:



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