Question

I came up to some degree, but not sure. i will post my notes after.

Answer 1

Note that sides AD and BE are perpendicular on the same side AC. So the angles CAD and CBE, both are equal to 90 degrees.

Beig the corresponding angles, ADC and BEC are also equal.

And the angle ACD is the common angle in both the triangles.

Therefore by the AAA criteria, the triangles CAD and CBE are similar.

So their corresponding sides must be proportional,

`\begin{gathered} (AD)/(BE)=(AC)/(BC) \\ \frac{4\sqrt[]{138}}{\sqrt[]{138}}=\frac{6\sqrt[]{3}+BC}{BC} \\ 4=\frac{6\sqrt[]{3}+BC}{BC} \\ 4BC=6\sqrt[]{3}+BC \\ 3BC=6\sqrt[]{3} \\ BC=2\sqrt[]{3} \end{gathered}`