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CEMC Fermat, 2024

Geometry Difficulty 4.5 AIME Find the answer Canada

In the diagram, point CC is
on side BDBD of quadrilateral ABDEABDE. Also, ABAB and EDED are perpendicular to BDBD, ∠ACB=60°\angle ACB = 60\degree, ∠CAE=45°\angle CAE = 45\degree, and ∠AEC=45°\angle AEC = 45\degree.

Figure 0

If AB=3AB = \sqrt{3}, what is the
perimeter of quadrilateral ABDE ABDE\,?

Pick one

Solution

We note first that △ACB\triangle ACB has a right angle and a 60°60\degree angle and so it is a 30°30\degree- 60°\,60\degree- 90°\,90\degree triangle.

Since AB=3AB = \sqrt{3}, then using the
known ratios of side lengths, we can see that BC=1BC = 1 and AC=2AC = 2.

Next, we note that △ACE\triangle ACE
has two 45°45\degree angles and so is
an isosceles right-angled triangle.

This means that CE=AC=2CE = AC = 2 and
∠ACE=90°\angle ACE = 90\degree.

Also, AE=2AC=22AE = \sqrt{2}AC = 2\sqrt{2}.

Further, since ∠BCD\angle BCD is a
straight angle, then ∠ECD=180°−∠ACB−∠ACE=180°−60°−90°=30°\angle ECD = 180\degree - \angle ACB - \angle ACE = 180\degree - 60\degree - 90\degree = 30\degree Since △CED\triangle CED has a 30°30\degree angle and a right-angle, it is
also a 30°30\degree- 60°\,60\degree- 90°\,90\degree triangle.

Using the known ratios of sides, since CE=2CE = 2, we have DE=1DE = 1 and
CD=3CD = \sqrt{3}.

Therefore, the perimeter of ABDEABDE is
AB+BC+CD+DE+AE=3+1+3+1+22=2+22+23AB + BC + CD + DE + AE = \sqrt{3} + 1 + \sqrt{3} + 1 + 2\sqrt{2} = 2 + 2\sqrt{2} + 2\sqrt{3}

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Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.