Question

4+9+14+19+.....+1004

Answer 1

 

$\displaystyle\\4+9+14+19+...+1004=?\\\\\text{Calculam numarul de termeni: }\\\\n=\frac{1004-4}{5}+1=\frac{1000}{5}+1=200+1=201~\text{termeni} \\\\\text{Aplicam formula lui Gauss:}\\\\S=\frac{n(1004+4)}{2}=\frac{201\times1008}{2}=201\times504=\boxed{\bf101304}$

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