Hello thereddevilsI've re-drawn the diagram (attached), so that (which I think is what you meant) looks more like the bisector of .

Then in 's(tangents from a point to a circle)'s are congruent (SAS)

( is angle bisector, given)

is common

Now - and I'll leave you to fill in the details - prove that 's are similar. Hence , and hence .

But (given). Therefore ... ?

Grandad