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In the lamp-post and shadow setup of Fig. 6.32, why are $\triangle ABE$ and $\triangle CDE$ similar? 
ATheir three sides are proportional
BOne angle is common and another pair are right angles
CThey are congruent by RHS
DTheir corresponding medians are equal
Answer & Solution
Correct answer: B. One angle is common and another pair are right angles
In $\triangle ABE$ and $\triangle CDE$, $\angle B=\angle D=90^\circ$ because both the lamp-post and the girl are vertical to the ground. Also, $\angle E$ is common. Therefore, the triangles are similar by the AA criterion.
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