Odpowiedź:
1) P = πr²
πr² = 9π
r² = 9
r = 3
2) πr² = 25π
r² = 25
r = 5
d = 2r = 2 × 5 = 10
3) Obw = 2πr
2πr = 10π
2r = 10
4) 2πr = 9π
2r = 9
r = 4,5
d = 2r = 2 × 4,5 = 9