First look at the naming of the sides of the triangle
Left down is A, Right Down is B, Top right is D, between B and D is C
the triangle ABD is a 30,60,90 triangle, meaning that if AB =10, then AD =20, and DB = 10
The triangle ACD is an isosceles triangle, thats because angle CAD = 30, and CDA =30
Now we know that side AC = x
The Triangle ABC is also 30,60,90 triangle meaning that if AC=X, then CB=x/2, and AB= (X/2)
at side DB, DC=X, and CB =x/2, and we found that DB = 10
so:
