Question

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

Answer 1

$a_n=a_1+r(n-1)$

r=3-(-2)=5

$43=-2+5(n-1) \\\\45=5(n-1) \\\\9=n-1 \\\\\boxed{n=10}$

Answer 2

Formula: an = a1 + (n - 1).r

an= 43
a1 = -2
n = ?
r = 5


43 = -2 + (n - 1).5
43 = -2 + 5n - 5
43 + 7 = 5n
50 = 5n
n = 50/5
n = 10


☆Espero ter ajudado!