Question

15 : c, d
Vă roooog , ajutați dau coroana și 100 puncte

Answer 1

c) 6+11+16+21+...+506=6+(6+1*5)+(6+2*5)+(6+3*5)+...+(6+100*5)=
6*101+5*(1+2+3+...+100)=6*101+5*(100*101)/2=6*101+5*50*101=
101*(6+250)=101*256=25856.

d) 4+9+14+19+...1004=4+(4+5*1)++(4+5*2)+(4+5*3)+...+(4+5*200)=
     4*201+5*(1+2+3+...+200)=
     4*201+5*(200*201)/2=4*201+5*100*201=201*(4+5*100)=
     201*(4+500)=201*504=101304.