Question

Sa se calculeze:
a) 25+26+27+...+60=
b) 11+12+13+...+50=
c) 21+22+23+...+70=
d) 28+29+30+...+80=
e) 76+77+78+...120=
f) 98+99+100+...+210=​
va rog ma ajutati la tema!

Answer 1

Răspuns:

Explicație pas cu pas:

a) 25+26+27+...+60=

60 - 25 + 1 = 36 termeni are suma

= 36 × ( 25+60) : 2 =

= 36 × 85 : 2 =

= 1 530

____________________________

b) 11+12+13+...+50=

50 - 11 + 1 = 40 termeni

= 40 × (11+50) : 2 =

= 20 × 61 =

= 1 220

_______________________

c) 21+22+23+...+70=

70 - 21 + 1 = 50 termeni

= 50 × (21+70) : 2 =

= 50 × 91 : 2 =

= 4 550 : 2 =

= 2 275

_______________________________

d) 28+29+30+...+80=

80 - 28 + 1 = 53 termeni

= 53 × ( 28 + 80 )  : 2 =

= 53 × 108 : 2 =

= 2 862

______________________

e) 76+77+78+...120=

120 - 76 + 1 = 45 termeni

= 45 × ( 76 + 120 ) : 2 =

= 45 × 196 : 2 =

= 4 410

____________________

f) 98+99+100+...+210=​

210 - 98 + 1 = 113 termeni

= 113 × ( 98 + 210 ) : 2 =

= 113 × 302 : 2 =

= 17 063