Jawabanmu

2014-02-25T20:47:35+07:00
= π(r1)² : π(r2)²
= (r1)² : (r2)²
=36 : 64

jadi
(r1)² = 36
(r1) = 6, 

(r2)² = 64
(r2) = 8
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perbandingan keliling
2π(r1) : 2π(r2)
6 : 8
3 : 4
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selisih keliling lingkaran
= 2π(r2) - 2π(r1)
= 2 x (3,14) x 8 - 2 x (3,14) x 6
= 50,24 - 37,68 
= 12,56
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perbandingan jari jari
=r1 : r2
=6 : 8
=3 : 4
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selisih jari jari
=r2 - r1
=8 - 6
=2