Question

S=1+3+5+7+........+259​

Answer 1

Explicație pas cu pas:

S=(2×1-1)+(2×2-1)+(2×3-1)+.....+(2×130-1)

S= 2×(1+2+3+...+130)-(1+1+1...+1)

1+1+1...+1 -de 130 ori = 130

1+2+3+..+n= n(n+1)/2

1+2+3+...+130=130×131/2 = 8515

S=2×8515-130

S=16900