Dik luas permukaan bola 7.850cm tentukan jari jari

Luas permukaan bola = 4×phi×r×r
7850 = 4× 3,14 ×r×r
7850 /( 3,14 ×4) = r×r
2500/4 = r×r
625 = r×r
25×25 = r×r

Jadi jari2 = 25

Lpbola=4 phi r^2
7850=4x3,14xr^2
r^2=7850:3,14x4
r^2=15700:2:157:50x4
=15700/2x50/157x4
=625
r=25