Question

A razão da P. A. em que a4 = 27 e a16 = 111 é: a) 3 b) 4 c) 5 d) 6 e) 7

Answer 1

Podemos utilizar o termo geral da PA.

$\boxed{\sf a_n~=~a_m~+~(n-m)\cdot r}$

Para n=16 e m=4, temos:

$\sf a_{16}~=~a_4~+~(16-4)\cdot r\\\\\\111~=~27~+~12\cdot r\\\\\\12r~=~111~-~27\\\\\\r~=~\dfrac{84}{12}\\\\\\\boxed{\sf r~=~7}~~ \Rightarrow~Letra~E$

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