I was drawing two tangent circle many as I could with integer radius. I notice there is some pattern, so i quickly observe and find out 4 formula for two tangent circle.

Assume that \(AC\) and \(AD\) is \(R\) , and \(BF\) and \(BE\) is \(r\). Now these are the formula that i have founded,\(\Large AP = \frac{R}{R + r} \times AB\)

\(\Large PB = \frac{r}{R+r} \times AB\)

\(\Large BQ = \frac{r}{R-r} \times AB\)

\(\Large AQ = \frac{R}{R-r} \times AB\)

Now to my question,

Why did this formula work? I just analysis a pattern.

Have you guys ever heard of this formula before?

## Comments

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TopNewestTriangles ADP and BFP are similar with ratio \(R : r\). Triangles ACQ and BEQ are similar with ratio \(R : r\). So \(AP : AB = AP : (AP + PB) = R : (R + r)\) by the similarity, and likewise with the rest. – Ivan Koswara · 11 months, 3 weeks ago

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– Rishabh Tiwari · 11 months, 3 weeks ago

Similarity of triangles must be used here as Ivan sir suggested, btw nice observation jason.!Log in to reply

– Jason Chrysoprase · 11 months, 3 weeks ago

Ohhh, i get itLog in to reply