Question

Alguém pode me ajudar?

Answer 1

$a_n=2n^2 + n\\ a_n=210\\\\ 2n^2 + n=210\\ 2n^2 + n - 210=0\\ \Delta=1^2-4.2.(-210)=1+1680=1681\\\\ n=\frac{-(1)\pm \sqrt{1681} }{2.2}\\\\ n=\frac{-1\pm 41 }{4}\\\\ n_1=\frac{-1+ 41 }{4}=\frac{40}{4}=10\\\\ n_2=\frac{-1- 41 }{4}=\frac{-42}{4}=\frac{-21}{2}\\\\ Tem \ 10 \ termos.$