Răspuns:
Explicație pas cu pas:
3 + 7 + 11 + ..... + 43 = 253
(43 - 3 ) : 4 + 1 = 11 termeni are suma
= 11 × ( 3 + 43 ) : 2 =
= 11 × 46 : 2 =
= 11 × 23 =
= 253
_________________________
1 + 3 + 5 + .... + 99 =
( 99 - 1 ) : 2 + 1 = 98 : 2 + 1 = 50 termeni are suma
= 50 × ( 1 + 99 ) : 2 =
= 50 × 100 : 2 =
= 50 × 50 =
= 2 500
____________________
7 + 14 + 21 + ..... + 2 023 =
= 7 × ( 1 + 2 + 3 + ...... + 289 ) =
= 7 × [ 289 × ( 1 + 289 ) : 2 ] =
= 7 × ( 289 × 290 : 2 ) =
= 7 × ( 289 × 145 ) =
= 7 × 41 905 =
= 293 335
