Find the Cosine of the Angle Between the Two Vectors $\langle 1,2 \rangle$

Multiple Choice

Find the cosine of the angle between the two vectors $\langle 1,2 \rangle$ and $\langle - 2,1 \rangle$ .

A) $\frac { 1 } { \sqrt { 2 } }$
B) 0
C) $\frac { 1 } { \sqrt { 3 } }$
D) 1
E) $\frac { 1 } { \sqrt { 5 } }$
F) $\frac { 1 } { 2 }$
G) $\frac { 4 } { 3 }$
H) $\frac { 3 } { 4 }$