Dados:
[tex]a_7=1458\\ q=-3[/tex]
Resolução:
[tex]\boxed{a_n=a_kq^{n-k}}[/tex]
[tex]a_7=a_1q^6\ \therefore\ 1458=a_1(-3)^6\ \therefore\\\\ 2(3^6)=a_1(3^6)\ \therefore\ \boxed{a_1=2}[/tex]
