Question

Calculati suma termenilor !Dau coroana​

Answer 1

Explicație pas cu pas:

(2×1+1)+(2×2+1)+....(2×40+1)

2×1+2×2+1.....2×40+40

2(1+2+.....40)+40

2×(40×41supra/2)+40

2×820+40

1680