Question

Se considera sirul de numere:75,78,81,84,......297,300,303.
a)Cate numere sunt in sir?
b)Care este suma lor?

Answer 1

  
[tex]\displaystyle \text{Se da sirul: 75, 78, 81, 84, ... 297, 300, 303} \\ \\ a)~~~ n = \frac{303 - 75}{3}+1 = \frac{228}{3}+1= 76+1 = \boxed{77~ de~numere} \\ \\ b)~~~ S = 75+78+81+84+ ... +297+ 300+303= \\ \\ = \frac{77(303+75)}{2}= \frac{77 \times 378}{2} = 77 \times 189 = \boxed{14553}[/tex]