Area of triangle - NOT?

jpanhalt

Joined Jan 18, 2008
11,087

MrChips

Joined Oct 2, 2009
30,711
IMHO @atferrari had the best answer. It's a 3-4-5 right triangle. No need to go to wikiwhatever. Moreover, I can do the math in my head. I am not so sure I can do a square root so easily.
The example under study in post #1 is easy because it is a right-angled triangle.
If it is not a right-angled triangle you cannot use that method. It then becomes more complex.

You can tell that the formula used in #1 is not correct if you apply dimensional units.
As @WBahn will always say, do the dimensional analysis.

area = length x length

You cannot arrive at an area by applying (length + length + length).
When you apply dimensional units to the square-root formula given in post #4 you will see:

area = square root of (length x length x length x length)

which reduces to:
area = length x length
 

atferrari

Joined Jan 6, 2004
4,764
The example under study in post #1 is easy because it is a right-angled triangle.
If it is not a right-angled triangle you cannot use that method. It then becomes more complex.
Yes. Is solved what was shown there, an angle that had no other possibility than being right-angled. Entered the page of the VBA guy later.

My teacher would be proud of me. :)
 

MrChips

Joined Oct 2, 2009
30,711
Presumably, what the creator of the calculator page on fortypoundhead did was follow the same instructions on the wikihow site. Unfortunately he/she read and replicated the first step of the calculation and did not realize that there was a second part to the calculation.
 
Presumably, what the creator of the calculator page on fortypoundhead did was follow the same instructions on the wikihow site. Unfortunately he/she read and replicated the first step of the calculation and did not realize that there was a second part to the calculation.
The VB code that is posted (in a zip file) at the fortypoundhead site references "fifth grade math" as the source of the formula (you can look yourself). I don't know what the process was other than a simple error, possibly just as you described. What puzzles me is that it has gone uncorrected.
 

WBahn

Joined Mar 31, 2012
29,978
I found this on WWW for the area of a triangle. Please tell me it is wrong.
https://www.fortypoundhead.com/showcontent.asp?artid=24319
View attachment 174865
It is definitely wrong. First, the units don't work out. Second, and answer of 60 for the area makes no sense for a triangle with sides of the length given. Clearly a 6 x 10 unit rectangle would fit easily inside that triangle.

The formula shown gives the semi-perimeter, which is then used in Heron's Formula (provided by MrChips above) to find the area. It has the two advantages of not requiring the determination of other lengths within the triangle and also working for any triangle, not just right triangles.
 

Thread Starter

AlbertHall

Joined Jun 4, 2014
12,345
In the end I didn't use the area of the triangle at all. I wanted to select the 'smallest' triangle and started by thinking that area would be the way to do that but a triangle can be very long and thin and so have a small area and yet still cover a lot of ground. In the end I used the perimeter as the measure to minimise and that seems to be working well.
 
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