Question

S=4+7+10+13....191
S=????

Answer 1

S = 4 + 7 + 10 + 13 + ...... + 190

→ stabilesc cati termeni are suma cu ratia = 3 ( 7 - 4 = 3;   10 - 7 = 3; .... )

( 190 - 4 ) : 3 + 1 = 186 : 3 + 1 = 62 + 1 = 63 termeni are suma

→ aplic formula sumei lui Gauss

S = 63 × ( 4 + 190 ) : 2

S = 63 × 194 : 2

S = 63 × 97

S = 6 111