Let side be "a" cm. So another side is (30-2a)/2=15-a S=ab=a(15-a)=15a-a^2 - parabola maximum when a = -15/-2=7.5 cm When a=7.5 all sides are 7.5 cm So it's a square. S=a*a=7.5*7.5=56.25 cm^2 - max There is no global minimun for S.(look at the graphic)
