Question

Se considera multimea M={0,4,8,12,16,20,24}. Sa se determine numarul tripletelor (a,b,c) cu proprietatea ca a,b,c ∈ M, a<b<c si a,b,c sunt in progresie aritmetica

Answer 1

a,b,c sunt in progresie aritmetica, deci b-a=c-b sau a+c=2b
tripletele sunt 0,4,8;0,8,16;0,12,24;4,8,12;4,12,20;8,12,16;8,16,24;12,16,20;16,20,24;
deci 9 triplete