Numa pa a soma dos seis primeiros termos e 12.sabendo que an=7 calcule a1
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Solução!
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sn=12
n=6
an=7
a1=?
![Sn= \dfrac{(a1+an)n}{2}\\\\\
12= \dfrac{(a1+7)6}{2}\\\\\
12=(a1+7).3\\\\\
12=3a1+21\\\\\
12-21=3a1\\\\\
-9=3a1\\\\\
a1= \dfrac{-9}{3} \\\\\\
a1=-3](https://tex.z-dn.net/?f=Sn%3D+%5Cdfrac%7B%28a1%2Ban%29n%7D%7B2%7D%5C%5C%5C%5C%5C%0A12%3D+%5Cdfrac%7B%28a1%2B7%296%7D%7B2%7D%5C%5C%5C%5C%5C%0A12%3D%28a1%2B7%29.3%5C%5C%5C%5C%5C%0A12%3D3a1%2B21%5C%5C%5C%5C%5C%0A12-21%3D3a1%5C%5C%5C%5C%5C%0A-9%3D3a1%5C%5C%5C%5C%5C%0Aa1%3D+%5Cdfrac%7B-9%7D%7B3%7D+%5C%5C%5C%5C%5C%5C%0Aa1%3D-3 "Sn= \dfrac{(a1+an)n}{2}\\\\\
12= \dfrac{(a1+7)6}{2}\\\\\
12=(a1+7).3\\\\\
12=3a1+21\\\\\
12-21=3a1\\\\\
-9=3a1\\\\\
a1= \dfrac{-9}{3} \\\\\\
a1=-3")
Boa noite!
Bons estudos!
Solução!
Dados!
sn=12
n=6
an=7
a1=?
Boa noite!
Bons estudos!
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