Maths Olympiad Prep

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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, $\$\angle
ACB = 60°60\degree,, \angle CAE =
45°45\degree,and, and \angle AEC =
45°$.45\degree\$.

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

Pick one

Solution

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

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

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

Further, since BCD\angle BCD is a
straight angle, then ECD=180°ACBACE=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 $CE =
2,wehave, we have DE = 1$ 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.