Question

Sa se afle suma S=5+10+15+...+525 va roog

Answer 1

S=5+10+15+....+525

S=5(1+2+3+.....+105)

S=5×(105×106)/2

S=5×105×53

S=525×53

S=27825

Answer 2

Rezolvare

S =5 +10 +15 +..... +525

Ne folosim de formula lui Gauss

n ×(n +1):2

Dăm factor comun pe 5

5 ×(1 +2 +3 +.... +105)

5 ×105 ×(105 +1) :2

5 ×105 ×106 :2

525 ×106 :2

55.650 :2

27.825

Răspuns :S=27.825