Vsferei=4pi Rla a3/3
R=d/2=12/2=6
Vsferei =4pi·6la cub/3=4pi·216/3=4pi·72=288pi dar Vsfera=Vcilindru
Vcilindru=piR1lapatrat·h⇒piR1la patrat·1,8=288pi⇒R1la patrat=288:1,8⇒R1la patrat=160⇒R1=4 radical din 10⇒diamerrul placii =2R1=2·4 radical din 10=8radicaldin10,