Will the perimeter and the area of a triangle ever equal one another?

Answer 1

Consider any triangle with given angles. If you expand it by a linear scale factor x, then its perimeter is multiplied by x, and its area by x2. When x is big, x2 is bigger than x. The area thus grows relative to the perimeter; as x tends to infinity, the ratio area/perimeter (call it R) tends to infinity. When x is small, x2 is smaller than x. The area thus shrinks relative to the perimeter; as x tends to zero, the ratio R tends to zero. For perimeter to equal area, R must equal 1. Since R is continuously defined, and (as we have just seen) it varies between zero and infinity, there must be some value of x that renders R = 1. This proves that an infinite number of triangles have perimeter equal to area, since our reasoning applied to triangles of any shape. To give one example, we'll find the equilateral triangle with perimeter equal to area. Set the length of a side equal to 2y. area = height x base / 2 = y2sqrt3 perimeter = 6y So, solve 6y = y2sqrt3 6 = ysqrt3 y = 6/sqrt3 = 2sqrt3 One more trivial example: if perimeter equals zero, then it definitely equals area.