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In the figure below, equilateral $ {\Delta} $ ABC lies in the x-y coordinate plane.

If A lies at the origin $(0,0)$ and B lies at $(b,0)$, what are the coordinates of C?

$ {(\cfrac { b }{ 2 } ,b)} $

$ {(b,b)} $

$ {(\cfrac { b }{ 2 } ,\cfrac { b }{ 2 } )} $

$ {(\cfrac { b\sqrt { 3 } }{ 2 } ,\cfrac { b }{ 2 } )} $

$ {(\cfrac { b }{ 2 } ,\cfrac { b\sqrt { 3 } }{ 2 } )} $