Jawabanmu

2014-08-29T14:50:58+07:00
Dik : L = 78 4/7 cm²
        π = 22/7
Dit : d ... ?
Jwb :
  L = 4 π r²
  78 4/7 = 4 . 22/7 . r²
  550/7 = 88/7 . r²
  r² = 550/7 : 88/7
  r² = 550/7 . 7/88
  r² = 550/88
  r² = 6,25
  r = √6,25
  r = 2,5 cm

Maka, d = 2 . r
             = 2 . 2,5
             = 5 cm
3 4 3
2014-08-29T14:51:55+07:00
78 4/7 = 1/4 x 22/7 x d x d
panjang diameter = 10