Question

Determine o número de termos da PA (-10, -5,...,435). *

Answer 1

$\large\boxed{\begin{array}{l}\sf(-10,-5,...,435)\\\sf a_1=-5~r=-5+10=5~a_n=435~n=?\\\sf a_n=a_1+(n-1)\cdot r\longrightarrow n=\dfrac{a_n-a_1}{r}+1\\\sf n=\dfrac{435-(-10)}{5}+1\\\sf n=\dfrac{435+10}{5}+1\\\sf n=\dfrac{445}{5}+1\\\sf n=89+1\\\sf n=90\end{array}}$