Question

Resolva a PA :
DADOS
a1 = 42
an = -12
n = 10
r = ?

Answer 1

an = a1 + ( n -1) . r
-12 = 42 + ( 10 -1) . r
-12 = 42 + 9 r -12
- 42 = 9 r
-54 = 9 r
r = 54/ - 9
r = -6

Razão da PA  = -6