Largest square in the corner of a right-angled triangle

Largest square in the corner of a right-angled triangle

IP 2
8 marks

Triangle \(ABC\) has \(\angle C=90^\circ\), \(CA=b\) cm and \(CB=a\) cm. A square \(CPQR\) of side \(s\) cm is drawn with \(P\) on \(CA\), \(R\) on \(CB\) and \(Q\) on \(AB\), as shown in the diagram.

  1. By considering triangles \(APQ\) and \(ACB\), show that \(s=\dfrac{ab}{a+b}\).[3]
  2. Find \(s\) when \(a=3\) and \(b=6\).[1]
  3. Prove that, for every such triangle, the square covers at most half of the area of the triangle, and state when it covers exactly half.[4]

Solution:

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Answer:(a) Shown (b) \(2\) cm (c) Ratio \(\dfrac{2ab}{(a+b)^2}\le\dfrac{1}{2}\) since \((a-b)^2\ge0\); exactly half when \(a=b\)

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