Question

Obtenha os três primeiros termos da PA na qual a7 = 12 e a14 = - 9​

Answer 1

$\large\boxed{\begin{array}{l}\sf a_{14}=a_7+7r\\\sf12+7r=-9\\\sf 7r=-9-12\\\sf7r=-21\\\sf r=-\dfrac{21}{7}\\\sf r=-3\\\sf a_7=a_1+6r\\\sf 12=a_1+6\cdot(-3)\\\sf a_1-18=12\\\sf a_1=12+18\\\sf a_1=30\\\sf a_2=a_1+r\\\sf a_2=30-3=27\\\sf a_3=a_2+r\\\sf a_3=27-3\\\sf a_3=24\\\sf os~tr\hat es~primeiros~termos~s\tilde ao~30,27~e~24\end{array}}$