Jawabanmu

2014-06-10T07:41:56+07:00
D² = p² - ( r1 + r2)²
20² = p² - ( 8 + 7 )²
400= p² - (15)²
400= p² - 225
P² = 400 + 225
P² = 625
P = 25 cm

Jarak pusat nya 25 cm