Respostas

  • Usuário do Brainly
2014-09-04T03:57:44-03:00
a_n=a_1+(n-1)r

a_{12}=a_1+11r

a_{14}=a_1+13r

a_{14}-a_{12}=a_1+13r-a_1-11r=2r.

Mas, a_{14}-a_{12}=-9-7=-16.

Com isso, r=-8 e a_1+11\cdot(-8)=7 e obtemos a_1=95.

(95, 87, 81)
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