Question

determine o 31° termo da P.A. (9,13,17,21...)

Answer 1

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$\sf r=13-9=4\\\sf a_{31}=a_4+27r\\\sf a_{31}=21+27\cdot4\\\sf a_{31}=21+108\\\huge\boxed{\boxed{\boxed{\boxed{\boxed{\sf a_{31}=129}}}}}$