Răspuns:
1) presupunem ca p(1) adevarat.. p(k) adevarat atunci demonstram p(k+1) adevarat
Explicație pas cu pas:
p(k+1)=(k+1)(3k+3+1)/2=(k+1)(3k+2)/2=3k^2+5k+2
=1+4+7+...+(3k-2)+[3(k+1)-2]
=p(k)+[3(k+1)-2]
=k(3k-1)/2+[3(k+1)-2]
=3k^2+5k+2
