A storage box with a square base must have a volume of 80 cubic centimeters. The top and bottom cost $0.20 per square centimeter and the sides cost $0.10 per square centimeter. Find the dimensions that will minimize cost. (Let x represent the length of the sides of the square base and let y represent the height. Round your answers to two decimal places.) x

Box dimensions:

x =  3.42 cm

y = 6.84 cm

C(min) = 14.04 $

Step-by-step explanation:

We need the surface area of the cube:

S(c)  =  2*S₁ ( surface area of top or base) +  4*S₂ ( surface lateral area)

S₁  = x²        2*S₁  = 2*x²

Surface lateral area is:

4*S₂  =  4*x*h                          V(c) =  80 cm³  =  x²*h          h  =  80/x²

4*S₂  = 4*80/x

4*S₂  = 320 / x

Costs

C (x)  =  0.2* 2*x²   +  0.1 * 320/x

Taking derivatives on both sides of the equation we get:

C´(x)  =    0.8*x   -  32/x²

C´(x)  =  0            0.8*x - 32/x²  = 0

0.8*x³  -  32  =  0            x³  =  32/0.8

x³  =  40  

x =  3.42 cm

h =  80/(3.42)²          h  = 6.84 cm

To find out if x = 3.42 brings a minimum value for C we go to the second derivative

C´´(x) =  64/x³       is always positive for  x > 0  

The C(min) = 0.4*(3.42)²  +  32/(3.42)

C(min)  =  4.68 +  9.36

C(min)  = 14.04 $

c. (0.6,-1.4)

step-by-step explanation:

hope this

correct choice is b

step-by-step explanation:

when you calculate the average rate of change of a function, you are finding the slope of the secant line between the two points. for the function the average rate of change from point to point can be calculated as

to find the average rate of change from day 2 to day 10, note that at day 2, 8 houses were sold, so a(2,8) and at day 10, 2 houses were sold, so b(10,2). thus,