nu adun-am aflam doar Nr de elemente repede va rog ​

Explicație pas cu pas:

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30=

55+155+255=465(30 elemente)

2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30=464(29 elemente)

9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30=429(22 elemente)

sper ca este corect

Răspuns:

Explicație pas cu pas:

a) 1 + 2 + 3 + .......... + 30 =

= 30 × ( 1+30) : 2 =

= 30 × 31 : 2 =

= 930 : 2 =

= 465

→ am aplicat formula sumei lui Gauss = nr. termeni ×(primul+ultimul termen) : 2

de la 1 la 30 sunt 30 de termeni

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b) 2 + 3 + ...... + 30 = 464

30 - 2 + 1 = 28 + 1 = 29 termeni are suma

= 29 × ( 2+29) : 2 =

= 29 × 32 : 2 =

= 928 : 2 =

= 464

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c)  9 + 10 + 11 + ........ + 30 =

30 - 9 + 1 = 21 + 1 = 22 termeni are suma

= 22 × ( 9 + 30 ) : 2 =

= 11 × 39 =

= 429