Notice the small 4 sided figure formed in the middle. It is actually a square.

The three purple lines and 1 shorter diagonal are all identical (they are diagonals of identical rectangles with length of 2 squares and breadth of 1 square)


Line COD cuts across this square's vertices and part of it forms the square's diagonal. Since a square is divided by its diagonal into 2 identical isosceles triangles, the angle on each side of the diagonal is 45°.

So x = 45

@J you're simply the best!

You are so great. And marvellous. AND make it so easy to understand . Thank you so much. You are

@AC Lim too. You are

@J and @AC Lim .. thank you all for helping us. Happy Good Friday holidays to you !!

Welcome. There are more ways to solve the question using angles and similar triangles.


The above method may require some working for proof. Check with your teacher what is required to be presented.

@AC thanks!

Working ? Really .. okok sure thank thank again. Happy Good Friday to you .

@Ivy, you are welcome.
@J Math Olympiad need correct answer and fastest way to solve.
In fact, I was thinking trigonometry method with sin, cos and tan...etc :)... But you solve it without calculation :), simply draw 4 lines :). haha!

Haha wanted to use trigo as well but the primary Olympiad probably not covered, so tried some construction

Thank you so much for your help. Hooray..

Woww this method is great too. I can try this out next time when I encounter similar question. Thank you ❤

U r most welcome