l = r + 5
Pb = 50π
Pb = πrl πrl = 50π /:π rl = 50 r(r + 5) = 50
r² + 5r - 50 = 0
Δ = 25 - 4 * 1 * (-50) = 25 + 200 = 225
√Δ = 15
r1 = (-5 - 15)/2 = -20/2 = -10 ∉ D
r2 = (-5 + 15)/2 = 10/2 = 5
r = 5
l = 5 + 5 = 10
odp. r = 5 i l = 10
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l = r + 5
Pb = 50π
Pb = πrl
πrl = 50π /:π
rl = 50
r(r + 5) = 50
r² + 5r - 50 = 0
Δ = 25 - 4 * 1 * (-50) = 25 + 200 = 225
√Δ = 15
r1 = (-5 - 15)/2 = -20/2 = -10 ∉ D
r2 = (-5 + 15)/2 = 10/2 = 5
r = 5
l = 5 + 5 = 10
odp. r = 5 i l = 10