What is ratio of the length $x$ to $y$ in quadrilateral $ABCD$?

81 Views Asked by At

Problem:

                           enter image description here

Here is what I've tried:

   enter image description here

I drew symmetry of $BC$ and $AB$ along $AC$. Now $AE$ is angle bisector of $\angle DAC$. It seems it is enough to only consider $\triangle ACD$ and segments in it, but I still can't see a connection between orange segment and green segment.

2

There are 2 best solutions below

2
On BEST ANSWER

As in comments, you already solved using law of sines. Here is a construction that shows $x = y$.

enter image description here

Extend $CB$ and drop a perp from $A$. Also drop a perp from $D$ to $AC$.

As $\angle ACE = 30^\circ, AE = AC/2$ and $\angle ABE = 50^\circ$. Also, as $\triangle ADC$ is isosceles triangle, $AH = CH = AC/2$.

That leads to $\triangle ABE \cong \triangle ADH$ (by A-S-A) and hence $x = y$.

0
On

Construct a circle that has centre $D$ and radius $DA$ as in the picture below and create a circumscribed angle $\angle APC$ on the large arc $AC$.

Then $\angle APC=50$. When observing the quadrilateral $ABCP$. You can easily say that it is cyclic which means points $A, B, C, P$ lies on the circumference of the same circle. This leads that points B and P are lying on the circumference of the circle that has radius $y$

Finally $BD=y$ as $\triangle ABD$ is equilateral $x=y$

enter image description here

@Math Lover's solution is more logical than mine.