Question

da factor comun si calculeaza suma 71+72+73+........210

Answer 1

71+72+73+........210 =
nr termeni   210-71+1=140
=(70+1)+(70+2)+(70+3)+....+(70+140)=
=70×140+(1+2+3+...+140)=
=70×140+140×141/2=
=70×140+70×141=
=70(140+141)=
=70×281=19670