Question

va rog 1 + 2 + 3 + ... +84=
2+4+6+...+110
1+3+5+...+101
39+40+41+...+110
5+10+15+20+...+2020
cine rapunde primu are coroana si like​

Answer 1

Răspuns:

1+2+3+...+84=(84x85):2=3570

2+4+6+...+110=2(1+2+3+...+55)=2((55x56):2)=2x1540=3080

1+3+5+...+101=(101-1):2+1=100:2+1=51

(101+5)x51:2=102x5:2=2601

5+10+15+...+2020=5(1+2+3+...+404)=5((404x405):2)=5x81810=409.050

Explicație pas cu pas:

Answer 2

Răspuns:

1+2+3+...+84=

=84×85:2=

=3570

2+4+6+...+110=

=2(1+2+3+...+55)=

=2×55×56:2=

=55×56=

=3080

1+3+5+...+101=

n=(101-1):2+1

n=51

(101+1)×51:2=

=102×51:2=

=2601

39+40+41+...+110=

n=110-39+1

n=72

39+40+41+...+110=

=(110+39)×72:2=

=5364

5+10+15+20+...+2020=

n=2020-5:5+1

n=404

5+10+15+20+...+2020=

=(2020+5)×404:2=

=409 050