CAT 2025 Quant was dominated by Algebra followed by Arithmetic. In Arithmetic, the questions were dominated by topics like Speed-time-distance, Mixture and Alligations. This year, there was a surprise. The questions from Geometry were relatively on the lower side as compared to the previous years. There were 8 TITA Qs this year. Overall this section was at a medium level of difficulty.
Question 18 : In \( \triangle A B C , A B = A C = 12 \mathrm {~cm} \) and \( D \) is a point on side \( B C \) such that \( A D = 8 \mathrm {~cm} \). If \( A D \) is extended to a point \( E \) such that \( \angle A C B = \angle A E B \), then the length, in cm , of \( A E \) is
In \(\triangle ABC\), \(AB=AC=12\) cm, so:
\[
\angle ABC=\angle ACB
\]
We are given:
\[
\angle ACB=\angle AEB
\]
Therefore:
\[
\angle ABC=\angle AEB
\]
Since side \(AB\) subtends equal angles at \(C\) and \(E\), the points \(A,C,E,B\) lie on a common circle, forming cyclic quadrilateral \(ACEB\).
In cyclic quadrilateral \(ACEB\):
\[
\angle AEC=\angle ABC
\]
Since \(\triangle ABC\) is isosceles:
\[
\angle ABC=\angle ACB=\angle ACD
\]
Therefore:
\[
\angle AEC=\angle ACD
\]
Also, \(\angle DAC=\angle CAE\) because \(AD\) and \(AE\) lie on the same line.
Hence, by AA similarity:
\[
\triangle ADC\sim\triangle ACE
\]
Corresponding sides give:
\[
\frac{AD}{AC}=\frac{AC}{AE}
\]
Substituting \(AD=8\) and \(AC=12\):
\[
\frac{8}{12}=\frac{12}{AE}
\]
\[
2AE=36\Rightarrow AE=18\text{ cm}
\]
Choice 3 is the correct answer.
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