Congruent Right Triangles: Lengths, Areas and Angles

Congruent Right Triangles: Lengths, Areas and Angles

Secondary 2

In the diagram, \(\Delta ABC\equiv \Delta CED\), \(AB=10\) cm, \(DC=25\) cm, \(\angle BAC=90{}^\circ \) and \(\angle ABC=60{}^\circ \). Find

  1. the length of \(CE\),
  2. the area of \(\Delta CED\),
  3. \(\angle CDE\),
  4. \(\angle BFE\).

Source check: the stated congruence makes the perpendicular legs of triangle \(ABC\) equal to \(10\) cm and \(25\) cm. These imply \(\angle ABC=\tan^{-1}(25/10)\approx68.2^\circ\), not the printed \(60^\circ\). Thus the complete set of givens is inconsistent. The length/area results below use the given sides and congruence; the angle results are conditional on the printed angles.

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Answer:\(\text{(a)}\ 10\text{ cm}\) \(\text{(b)}\ 125\text{ cm}^2\) \(\text{(c)}\ 30^\circ\) \(\text{(d)}\ 90^\circ\) Results are conditional as explained in the source check; the complete printed givens are inconsistent.

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