Question

Calculati urmatoarele sume:

D)1+2+3+...+124; E)1=2=3=...500;
G)5+6+7+...+81; I)317+318+319+...400

Answer 1

D)1+2+3+...+124=124×125/2=7750

E)1+2+3+...+500=500×501/2=125250

G)5+6+7+...+81=1+2+3+4+5+6+7+...+81-(1+2+3+4)=
=81×82/2-10=3321-10=3311

 
I)
nr termeni 400-317+1=84
317+318+319+...400 =317+(317+1)+(317+2)+...(317+83)=
=317×84+(1+2+...+83)=26628+83×84/2=26628+3486=30114