Respuesta :

Answer:

[tex]the \: common \: difference \: is \: - 10[/tex]

Step-by-step explanation:

[tex] - 9 - 10 = - 1[/tex]

[tex] - 1 - 10 = - 11[/tex]

[tex] - 11 - 10 = - 21[/tex]

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