Answer:
The dimensions are 32 ft by 16 ft
Step-by-step explanation:
Area of the coffee and recreation room=512 square foot
LB=512
L=512/B
Perimeter of the Room = Perimeter of north wall+Perimeter of east wall+ Perimeter of west wall =L+2B (West and East are opposite)
Cost of the Perimeter=16L+4(2B)
[tex]C(B)=16(\frac{512}{B})+8B\\C(B)=\frac{8192+8B^2}{B}[/tex]
To minimize cost, first, we take the derivative of C(B)
Using quotient rule
[tex]C^{'}(B)=\frac{8B^2-8192}{B^2}[/tex]
Setting the derivative equal to zero
[tex]8B^2-8192=0\\8B^2=8192\\B^2=1024\\B=32 ft[/tex]
[tex]L=\frac{512}{B}=\frac{512}{32}=16ft[/tex]
The dimension of the cheapest recreation area will be 32 ft by 16 ft