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calculează suma 10 +11+12......99

Răspuns :

1+2+3+...+9=9•10/2=45
1+2+3+...+99=99•100/2=4950
10+11+12+...+99=4950-45=4905
10 + 11+12+......+99 =
aflam cati termeni are sirul:
99 - 10 + 1 = 90
= (10+99) × 90 : 2 =
= 109 × 45 =
= 4 905