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Finding an Input To Match an Output

GRE-GN9CKE

A function $f(x)$ takes an input and turns it into its reciprocal. If $f(x)=-2.5$, what must $x$ be?

A

$\cfrac { 2 }{ 5 } $

B

$\cfrac { 5 }{ 2 } $

C

$-\cfrac { 2 }{ 5 } $

D

$-\cfrac { 5 }{ 2 } $