Question

Quantos termos compõem PA finita (7,2...-38) ?

Answer 1

$a_n=a_1+(n-1)*r\\\\ -38 = 7+(n-1)*-5\\\\ -38 -7 = (n-1)*-5\\\\ -45=-5(n-1)\\\\ (n-1)=\frac{-45}{-5}\\\\ (n-1)=9\\\\ n=9+1\\\\ \boxed{\boxed{n=10} }$

Essa PA possui 10 termos.