(2x-15) | 15 înseamnă (2x-15) divide 15.
=> 15/(2x-15) ∈ Z => 2x-15 ∈ D₁₅ =>
=> 2x-15 ∈ {-15,-5,-3,-1,1,3,5,15} => 2x ∈ {0,10,12,14,16,18,20,30} =>
=> x ∈ {0,5,6,7,8,9,10,15}
=> y = 0+5+6+7+8+9+10+15 = 60
=> Biletul costă 30 lei.
Explicație pas cu pas:
(2x-15)|15
(2x-15)|(2x-15)
(2x-15)∈D{15}
(2x-15)∈{-15,-5,-3,-1,1,3,5,15} |+15
2x∈{0,10,12,14,16,18,20,30} |:2
x∈{5,6,7,8,9,10,15}
y=5+6+7+8+9+10+15=11+15+19+15=26+34=60
y/2=60/2=30 lei costa un bilet
Bafta!
