Jawabanmu

2014-09-12T21:52:59+07:00
L = 4 \pi  r^{2}

diket, 
     d = 21 cm
     r = 10.5

L = 4 x 3,14 x 10.5 x 10.5
   = 1384,74  cm^{2}
2014-09-12T21:53:14+07:00
Luas kulit bola = 4πr²
                       = 4*22/7*21/2*21/2
                       = 1386 cm²