Jawabanmu

2014-05-11T06:58:50+07:00
(R-r) = √Jarak² - garis persekutuan luar²
(R-r) =√ 13²-12²
(7-r) = √169-144
(7-r) = √25
(7-r) =5 cm
     r= 7cm -5 cm
      = 2cm
2014-05-11T09:06:16+07:00
R-r = √s²- l² <=> 7-r = √13²-12² <=> 7-r = √169-144 <=>7-r = √25 <=>7-r = 5cm <=> r = 7-5 = 2cm {semoga membantumu} :D