Răspuns:
a) 1x2/1 + 1x2x3/1x2 +...+ (n+1) *n!/ n!= 2+3+ ...+ (n+1)=1+2+3 +...+n=
=n x ( n + 1 ) : 2
b) [tex]\frac{2n(2n-1)! }{(2n-1) !}[/tex] + [tex]\frac{(2n-1) (2n-2)! }{(2n-2)!}[/tex] + ...+ [tex]\frac{(n+1) n!}{n!}[/tex]= 2n+ (2n-1) +...+ (n+1)=
n! = n×(n-1)!
