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 $

answer: standard form is ax^2 + bx + c = 0

step-by-step explanation:

standard form is ax^2 + bx + c = 0

(2x + 1)(x - 2) = 0

distribute to get into standard form

2x^2 - 4x + x - 2 = 0

2x^2 - 3x - 2 = 0

a = 2, b= -3, c = -2

a is your answer