Radii of 2 circles are 16 cm and 8 cm. Find the distance between their centres if they touch internally.
8 cm
Consider 2 circles, one with centre 'O', and another with 'O1'.
Radius of the bigger circle = r1 = 16 cm
Radius of the smaller circle = r2 = 8 cm
The 2 circles touch each other at X internally.
OX = r1 = 16 cm
O1X=r2 = 8 cm
Distance between their centres =OO1=XO−XO1
=r1−r2
= 16 - 8
= 8 cm