Question

A rectangular lot is bounded on one side by a river and on the other three sides by a total of 80m of fencing. Find the dimensions of the lot with the largest possible area

Answer 1

Hello,

Let 's a the width,
b the heigth

2a+b=80==>b=80-2a

Area=A(a,b)=a*b=a*(80-2a)
=-2a²+80a
=-2(a²-2*20a+20²-20²)
=-2(a-20)² +800
Area is maxi if a=20 and area max=800