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8) p² = l² + (R–r)²

15² = 12² + (11–r)²

81 = (11–r)²

9 = 11–r

r = 2

9) s = (a+b+c)/2

= (9+12+15)/2

= 18

L = ½ a t

= ½ x 9 x 12

= 54

Jari² lingk dalam (r)

r = L/s

= 53/18

= 3 cm

Jari² lingk luar

R = abc / 4L

= 9 x 12 x 15 / (4 x 54)

= 7½ cm