A land owner is planning to build a fenced-in, rectangular patio behind his garage, using his garage as one of the "walls." He wants to maximize the area using 80 feet of fencing. The quadratic function A(x)=x(80−2x) gives the area of the patio, where x is the width of one side. Find the maximum area of the patio.

 800 feet²

Step-by-step explanation:

Lets remove the brackets from the function's expression

A(x) = -2x²+80x

So we got the quadratic function and we have to find the x that corresponds to function's maximum. Let it be X max

As we know Xmax= (X1+X2)/2 , where X1 and X2 are the roots of the function A(x)

Lets find X1 and X2

x(80-2x)=0

x1=0   80-2*X2=0

x2=40

So Xmax= (0+40)/2=20

So Amax= A(20)= 20*(80-2*20)=20*40=800 feet²