Hello all, the question I am trying to prove is as follows:

Let

be the circle

and let

aand put

where

Find necessary and sufficient conditions in terms of

that

be tangent to

at

Now if

was tangent to the circle

at the point

,

and

(i.e. the line segment from

to

, which has distance

) would have to be perpendicular.

i.e. triangle ACO, (where O is any point

where

on

) is a right triangle.

However using the Pythagorem theorem on the sides, doesnt seem to help me find what

is.

Can anyone offer me any advice on this problem please?