Answer: 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