A closed rectangular box with a square base is to have a volume of 512 cm

MATHEMATICS · Single correct · A Level · Mathematics · Differentiation · Differentiation

Problem

^{3}

. The material for the base costs twice as much per cm

^{2}

as the material for the sides and the top. Which of the following is the value of the base side

x

(in cm) that minimises the total cost of the box? (a)

9

(b)

7

(c)

6

(d)

8