Question

Cum se rezolva exercitiul 12,punctele b,c??

Answer 1

b) ab+bc+ca=10a+b+10b+c+10c+a
                    =11a+11b+11c
                    =11(a+b+c), deci e divizibil cu 11

c)1a1-1a+8=100+10a+1-10-a+8
                  =90+9a+9
                  =99+9a
                  =9(11+a),  deci e divizibil cu 9