Question

Calculati suma primilor 100 de termeni ai sirului : 1,8,15,22,29,.....

Answer 1

aici e progresie aritmetica 
$S_{100}= \frac{2 a_{1}+(n-1)r }{2}n$
$S_{100}= \frac{2+99*7}{2}100=(2+ 693)*50=695*50= 34750$