Let the radius of the first circle be r1

and second circle be r2.

third circle be R.

Given,

r1=8cm.r2=6cm.

A/q.

phi R^2=phi r1^2+phi r2^2.

phi R^2=phi(8^2+6^2).

R^2=64+36

R^2=100

R=10.

therefore the radius of the third circle of 10.CM.

HOPE IT HELPS YOU