Question

a soma dos 10 primeiros termos da PA (2,5,...)

Answer 1

(2,5,8,11,14,17,20,23,26,29)

2+5+8+11+14+17+20+23+26+29 = 155

Answer 2

Resolução da questão pela fórmula geral da PA, veja como se procede:

$\textsf{Organizando~os~dados:}\\\\\\ a_{1} = 2\\\\ r = a_{2}-a_{1}~=\ \textgreater \ ~r = 5-2~\therefore~r=3\\\\ n = 10\\\\\\ a_{n} = a_{1}+(n-1)~\cdot~r\\\\ a_{10} = 2+(10-1)~\cdot~3\\\\ a_{10} = 2+ 9~\cdot~3\\\\ a_{10} = 2+27\\\\ \\ \textt{a_{10} = 29}.\\\\\\ \textsf{Aplicando~a~soma~dos~termos~da~PA:}\\\\\\\ s_{n} = \dfrac{a_{1}+a_{n}}{2}}\\\\\\ S_{10} = \dfrac{(2+29)~\cdot~10}{2}}\\\\\\ S_{10} = \dfrac{31~\cdot~10}{2}}\\\\\\ S_{10} = \dfrac{310}{2}}\\\\\\\ \large\boxed{\boxed{\boxed{\boxed{S_{10} = 155.}}}}}}}$

Espero que te ajude. :-).