Calculating Area of a triangle with no angles

Rudolph Claus · 03-11-2005 06:56PM #1

How do i calculate the area of the triangle which has 3 sides naturally enough, measuring 4m, 1.5m and 3m in size.

Its a non right angle triangle so cant use 1/2base * perpendicular height.
I also cant use the SINE rule to work out some angles as i`d need at least 1 angle to implement the SINE rule formula.

Am i missing something simple or obvious here?

All help is appreciated.:)

dudara · 03-11-2005 06:59PM

Three sides are a, b and c, then

area = SQRT(s*(s-a)*(s-b)*(s-c))

where s = (a+b+c)/2

unkel · 03-11-2005 07:10PM

dudara wrote:

Three sides are a, b and c, then

area = SQRT(s*(s-a)*(s-b)*(s-c))

where s = (a+b+c)/2

That's handy to know!

I did it the basic way, by splitting the triangle into two right-angled triangles which lets you calculate the height of the triangle and lengths of the two parts that now form the base. Result is same

dudara · 03-11-2005 07:16PM

I'm pretty sure that it's in the log tables

Rudolph Claus · 05-11-2005 08:11PM

Thanks for the solutions lads.
I checked the log tables already, it only has the basic formula 1/2base *perpendicular height.
It shows the Sine rule too, but doesnt mention that formula that you gave, Dudara.

dudara · 06-11-2005 02:29PM

I've an ancient copy of the log tables, that I've had since my Junior Cert and it was my uncle's prior to that. (My Gran never threw anything away!). It's on page 6 of mine for reference's sake, in the left hand column.

Might have been cut from newer editions

Rudolph Claus · 07-11-2005 04:24PM

I've an ancient copy of the log tables, that I've had since my Junior Cert and it was my uncle's prior to that. (My Gran never threw anything away!). It's on page 6 of mine for reference's sake, in the left hand column.

Might have been cut from newer editions

Your dead right actually, dudara
I missed that somehow.

Did ye actually calculate the area out, i get 1.91metres squared but that seems a bit small?

@unkel
And having another look at it, i dont think you can split it down the middle to make 2 right angled triangles as the base is 4m, but the other 2 sides are at an angle and dont allow you to split it directly down the middle. If you do try split it, how do you know how long each bit of the baseline are, and how do you know the height of the perpendicular line.

dudara · 07-11-2005 04:32PM

No, 1.91 m^2 is right.

Nukem · 07-11-2005 06:33PM

Shamooaaan mutha ****a - link
Also am i missing something why not draw the thing and get the angles from that. Will do it CAD later for you if you wan?............hungry now:D

Nukem

Calculating Area of a triangle with no angles

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