Question

Quantos termos tem a P.A (-100;-99;...;19) ?

Answer 1

$a_{1} = -100 a_{n} = 19 r = 1 n = ?$

termo geral da P.A:
$a_{n} = a_{1} + (n-1) * r$ 
19 = -100 + (n-1) * 1
19+100 = n-1
119+1 = n
n = 120 termos

Answer 2

an= a1+ (n-1).r∴ 19= -100+(n-1).1∴ 19= -100+n-1∴ 19+100+1=n∴ n=120