Question

Determinati numerele naturale ab care au proprietatea ca ab-b=a*b+a

Answer 1

ab-b=a·b+a

10a+b-b=a(b+1)

10a=a(b+1) => b=9

a∈{1,2,3,4,.....,9}

ab∈{19, 29, 39, 49, .....,99}