Waste less time on Facebook — follow Brilliant.
×

Triangles with equal perimeter and area

Interesting problem that I'd like to share:

Find all triangles whose side lengths are integers such that the area equals perimeter.

[ Note: you can find the answer on google if you so desire. ]

Note by C Lim
4 years, 1 month ago

No vote yet
4 votes

Comments

Sort by:

Top Newest

One approach is the heron's formula by which we get a diophantine equation.

Another approach I have thought of is that for scalene triangles with side lengths \(a,b,c\), we must have that :

\(abx=2y(a+b+c)\)

Where \(sin \theta=\frac{x}{y}\) and \(x,y\) and are co-prime positive integers such that \(x<y\), and \(\theta\) is the angle between \(a\) and \(b\).

If we consider any isosceles triangle with integer side lengths \(a,b,b\) after doing some algebra we get that:

\(b=\frac{a(a^2+1)}{2(a^2-1)}\)

But this is not possible because of the triangle inequality:

We can use that since \(2b>a\)

By which we get a contradiction that \(-1>1\)

Obviously there will be no equilateral triangles that satisfy this. Aditya Parson · 4 years, 1 month ago

Log in to reply

×

Problem Loading...

Note Loading...

Set Loading...