Răspuns:
(a,b)∈{(7;28), (14;21), (21;14), (28;7)}
Explicație pas cu pas:
a=7k, b=7t
a+b=35, ⇒7k+7t=35, ⇒7(k+t)=35, ⇒k+t=5
k∈{1,2,3,4}
t∈{4,3,2,1}
⇒a∈{7·1, 7·2, 7·3, 7·4}={7, 14, 21, 28}
⇒b∈{7·4, 7·3, 7·2, 7·1}={28, 21, 14, 7}
⇒(a,b)∈{(7;28), (14;21), (21;14), (28;7)}
