Question

S1= 1-2+3-4+.......+2019-2020​

Answer 1

Răspuns:

S=1+3+5+......+2019)-(2+4+6+.....+2020)=1010²-2(1010×1011)/2=1020100-1010×1011=1020100-1021110=-1010

se aplică formula Ghaus.

S=1+3+5+...+15=[(15+1)/2]²=(16/2)²=8²=64

S=n²

S=2+4+6+....12=2(1+2+3+...+6)=2[6×(6+1)]/2=2×3×7=42

S=n(n+1)/2