*=ori
1*2*3=[tex]\frac{1*2*3*4}{4}[/tex],6=6. Se presupune ca egalitatea
1*2*3+2*3*4+........+n*(n+1)*(n+2)=[tex] \frac{n*(n+1)*(n+2)*(n+3)}{4}[/tex]
si se arata ca ea implica egalitatea
1*2*3+2*3*4+...+n*(n+1)+(n+1)*(n+2)*(n+3)=[tex]\frac{(n+1)*(n+2)*(n+3)}{3}.[/tex]
In adevar
1*2*3+2*3*4+........+n*(n+1)+(n+1)*(n+2)*(n+3)=[tex]\frac{n*(n+1)*(n+2)*(n+4)}{4}+(n+1)*(n+2)*(n+3)= \\ (n+1)*(n+2)*(n+3)*(\frac{n}{3}+1)= \\ \frac{(n+1)*(n+2)*(n+3)*(n+4)}{4}.[/tex]
Asadar egalitatea este adevarata pentru orice n natural.
Sper ca te-am ajutat!
E bine?