The Radius of Curvature of Y = Cos X at $\frac { 1 } { 2 \sqrt { 2 } }$

Multiple Choice

The radius of curvature of y = cos x at (?, -1) is

A) 1
B) $\frac { 1 } { 2 \sqrt { 2 } }$
C) $\frac { 2 } { 5 \sqrt { 5 } }$
D) $\frac { 2 } { 17 \sqrt { 17 } }$
E) $\frac { 7 } { 125 }$