Question

calculati urmatoarele sume:
1+2+3+......+30
2+3+4+.....+30
9+10+11+.....+30​

Answer 1

1+2+3+...+30=

=(30×31)/2=

=15×31=465

2+3+4+...+30=

=(1+2+3+...+30)-1=

=465-1=464

9+10+11+....+30=

=(1+2+3+...+30)-(1+2+3+...+8)=

=465-(8×9)/2=

=465-4×9=

=465-36=429

Answer 2

Răspuns:

Explicație pas cu pas:

1+2+3+......+30 =30×31/2=15×31=465

2+3+4+.....+30 =1+2+3+.........+30=465-1=464

9+10+11+.....+30​=1+2+3+......+30-(1+2+....+8)=465-8×9/2=465-36=429