Answer
$4-||u||=4-2\sqrt 5=2(2-\sqrt 5)$
Work Step by Step
$||u||=\sqrt {u·u}=\sqrt {⟨-4,2⟩⋅⟨-4,2⟩}=\sqrt {(-4)^2+2^2}=\sqrt {16+4}=\sqrt {20}=\sqrt {4(5)}=2\sqrt 5$
$4-||u||=4-2\sqrt 5=2(2-\sqrt 5)$
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