Question

3. Calculați următoarele sume: a) 2+4+6+…+88; b) 3+6+9+…+333; c) 5+10+15+…+2020; d) 8+16+24+…+800.​

Answer 1

Explicație pas cu pas:

a) 2+4+6+…+88=2(1+2+3+...+44)=2(1+44)*44:2=45*44=1980

b)3+6+9+…+333=3(1+2+3+...+111)=3(1+111)*111:2=112*333:2=56*333=18648

c) 5+10+15+…+2020=5(1+2+3+...+404)=5(1+404)*404:2=5*405*202=409050

d) 8+16+24+…+800=8(1+2+3+...+100)=8(1+100)*100:2=808*50=40400