Question

8+9+10+.....+54 please

Answer 1

1+2+3+....+54-(1+2+...+7)=54×55/2-7×8/2=27×55-7×4=1485-28=1457

Answer 2

Răspuns

Explicație pas cu pas:

I:   Aflam cati termeni contine suma: 54-8+1=46+1=47.

Aflam suma dintre cel mai mare si cel mai mic termen: 8+54=62.

8+9+10+...+54=(8+54)·47/2=62·47/2=31·47=1457.

II)   Putem afla suma scriind suma ca diferenta a doua sume tip Gaus si aplicam formula Sₙ =n(n+1)/2.

8+9+10+...+54=S₅₄-S₇=54·55/2-7·8/2=27·55-28=1485-28=1457.