Topic: From the triangle inequality to the isoperimetric inequality Abstract: Starting from the fact that the sum of the lengths of two sides of a triangle is greater than that of the third side, we will study a series of shape optimization problems for polygons and, finally, deduce the classical isoperimetric inequality in the plane. The talk will be accessible to those with a familiarity with plane geometry (triangles) and elementary notions of analysis like `supremum,' `limits' and `continuity'.