Question

daca stiti va rog sa ma ajutati: 11+22+33+.........+198

Answer 1

S=11+22+33+.........+198 =11×(1+2+3+.....+18)=11×S1

S1=(1+2+3+.....+18) - suma Gauss cu formula de calcul : S1= [n(n+1)]:2 unde n este ultimul termen al sumei

S1=[18×(18+1)]:2=171

S=11×S1=11×171=1881

S=11+22+33+.........+198 =1881

Answer 2

11+22+33+.........+n=n(n+1):2

11+22+33+.........+198=
=11(1+2+3+..18)
=11·18·19:2
=1881