Question

Determinati multimea
A={X apartine N/3x+12 supra 21, este fractie subunitara
repede dau coroana

Answer 1

x∈N astfel incat 
3x+12/21 =fractie subunitara deci
3x+12<21
3x<9
x<3⇒x∈{0,1,2}
A={0,1,2}