



 
Hi Mark, I drew two circles with centres $A$ and $B$ that are tangent to each other at the point $P.$ I joined $A$ and $B$ to $P$ and drew the common tangent line $ST.$ Since $AP$ is a radius of the small circle and $PT$ is tangent to the circle, the angle $APT$ is a right angle. Similarly the angle $TPB$ is a right angle. Thus $AB$ is a straight line. This is the key to your problem. See if you an solve the problem and write back if you need more assistance. Penny  


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