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  • Perplex
    IB Math AASL
    /
    Differentiation
    /

    Problem Bank

    [Maximum mark: 19]

    Anne is designing a gift box in the shape of a right triangular prism. In order for the box to be shipped, the longest side of the front face of the box must be ​1m.

    <ul>
<li>A right triangular prism is shown in perspective, with a peach-colored triangular top face and brown rectangular side faces.</li>
<li>The longest slanted edge of the triangular top face has a double-headed arrow labeled “1 m.”</li>
<li>A vertical double-headed arrow along the left edge is labeled “p m.”</li>
<li>A horizontal double-headed arrow along the long side face is labeled “q m.”</li>
<li>A blue ribbon-like band wraps around the box, visible as a vertical strip on the left face, continuing across the top face and down the right side, forming a branching shape on the top.</li>
</ul>

    Let the other side lengths of the box be ​p​ and ​q. Anne's company also sells wrapping paper. Hence, in order to maximize profits, Anne wants to maximize the surface area of the box.

      1. Find the perimeter, ​P​ of the front (triangular face) of the box in terms of ​p​ and ​q.

        [1]
      2. Show that ​P=1+p+√1−p2​.

        [2]
    1. Find ​dpdP​.

      [4]
    2. Find the value of ​p​ maximizing perimeter.

      [2]
    3. Give an expression for the area of the triangle in terms of ​p.

      [3]
    4. Show that the value of ​p​ maximizing the perimeter also maximizes the area.

      [5]
    5. Hence find the value of ​p​ maximizing the surface area of the box.

      [2]

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