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Find the cosine of the angle formed between the positive x-axis and the line segment from the origin that contains the point $(8, -4)$.

$-\cfrac { \sqrt { 5 } }{ 2 } $

$\cfrac { \sqrt { 5 } }{ 2 }$

$-\cfrac { \sqrt { 5 } }{ 5 } $

$-\cfrac { 2\sqrt { 5 } }{ 5 } $

$\cfrac { 2\sqrt { 5 } }{ 5 } $