Question

Numa PG Temos a5=162 e q=-3.calcule a1 e a7

Answer 1

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se:  a₅=162    e q= -3

$a_n=a_1.q^{n-1} \\ \\ 162=a_1.(-3)^{{5-1} } \\ \\ 162=a_1.(-3)^4 \\ \\ 162=a_1.81 \\ \\ a_1=162\div81 \\ \\ a_1=2$


$a_7=a_1.q^{n-1} \\ \\ a_7=2.(-3)^{7-1} \\ \\ a_7=2.(-3))^6 \\ \\ a_7=2.(729) \\ \\ a_7=1458$