WJEC Unit 1 Specimen — Question 14

Exam BoardWJEC
ModuleUnit 1 (Unit 1)
SessionSpecimen
TopicDifferentiation Applications
TypeProve constraint relationship

14. The diagram below shows a closed box in the form of a cuboid, which is such that the length of its base is twice the width of its base. The volume of the box is \(9000 \mathrm {~cm} ^ { 3 }\). The total surface area of the box is denoted by \(S \mathrm {~cm} ^ { 2 }\).
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  1. Show that \(S = 4 x ^ { 2 } + \frac { 27000 } { x }\), where \(x \mathrm {~cm}\) denotes the width of the base.
  2. Find the minimum value of \(S\), showing that the value you have found is a minimum value.