Question

em uma PA o 3 termo vale 36 e o 7 termo vale 56. O valor do 20 termo é:
a)11
b)121
c)131
d)200
e)211​

Answer 1

Resposta:

Letra B

Explicação passo-a-passo:

$a_n=a_k+(n-k)r,~~k<n\\\\a_7=a_3+(7-3)r\\\\a_7=a_3+4r\\\\56=36+4r\\\\56-36=4r\\\\20=4r\\\\r=\frac{20}{4}\\\\r=5\\\\a_2_0=a_3+17r\\\\a_2_0=36+17.5\\\\a_2_0=36+85\\\\a_2_0=121$