Jawabanmu

2014-04-20T14:58:05+07:00
R =  \sqrt{s(s-a)(s-b)(s-c)÷s
r =  \sqrt{21(21-13)(21-14)(21-15)÷21
r = 4

dima s = 1/2 keliling segitiga = 1/2 42 = 21