Question

Quantos elementos tem a P.A. finita ( -2,3...,43) ?

Answer 1

An = A1 + (n -1) * r

An = 43
A1 = -2

r = 3 - ( -2) = 5

43 = -2 + (n-1) * 5

43 = -2 + 5n - 5

43 + 2 + 5 = 5n

50 = 5n

50/5 = n

n = 10

P.A. de 10 termos e são eles

(-2,3,8,13,18,23,28,33,38,43)

Answer 2

$a_n=a_1+(n-1).r\\ \\ 43=-2+(n-1)5\\ \\ 43=-2+5n-5\\ \\ 5n=43+7\\ \\ 5n=50\\ \\ \boxed{n=10}$