Jawabanmu

2014-06-09T20:05:33+07:00
L²=p²-(R-r)²
12²=13²-(R-2)²
144= 169-(R-2)²
(R-2)²= √169-144
R-2 = 5
R = 5+2
R = 7 cm
2014-06-09T20:07:11+07:00
(R-r)2 = S2 - l2
= 169-144 = 25
R-r = 5
R = 7 cm