Question

If two circles with radii $10$ and $6$ respectively touch internally, then find the distance between their centres.

Answer 1

Let the radii of two circles be $R_1$ and $R_2$.
$\therefore$ $R_1=10$ and $R_2=6$
If two circles are touching internally then the common point lies on the line joining their centres.
Therefore, distance between their centres is $R_1-R_2$
$=10-6$
$=4$