Yes,  the shape could be a triangle.

It could be, but it doesn't have to be.

For example, let's say you had an equilateral triangle with sides that are all 6 units long.

The ratio of the side (6) to the total perimeter (18) is 1:3.

But you could construct other shapes that would work.

For example, let's say you had a rectangle that was 8 x 4.

One side is 8. The total perimeter is (8 + 4 + 8 + 4 = 24).

The ratio of one side (8) to the total perimeter (24) is 1:3.

Many other shapes could work too. For example, take a pentagon that has sides of 1, 2, 3, 4 and 5. Compare the middle side (3) to the total perimeter (15). Again it is a 1:3 ratio.

So as long as you make one side be 1/3 of the total perimeter, many shapes could work. But *all* equilateral triangles must work.

Yes

side of a equilateral to its perimeter is 1:3