1. The problem statement, all variables and given/known data show that for any triangle inscribed in a circle with radius r , the equilateral triangle has the largest perimeter. I'm supposed to use the larangian method. 2. Relevant equations 3. The attempt at a solution ok so my problem is forming an equation for the perimeter in terms of x and y. basically the constraint is to maximize perimeter with respect to the circle x^2 + y^2 = r so if a b c are the sides of the triangle, how can I form an equation for each side with respect to x and y? The distance from the origin to each vertex is r. But I'm not sure how to get an equation for the distance of each side. I just want some hints.