The sine of the angle between the vectors a =3 i + j +2 k and b = i + j +2 k is:

The sine of the angle between the vectors $\displaystyle \vec{a}=3 \hat{\mathrm{i}}+\hat{\mathrm{j}}+2 \hat{\mathrm{k}}$ and $\displaystyle \overrightarrow{\mathrm{b}}=\hat{\mathrm{i}}+\hat{\mathrm{j}}+2 \hat{\mathrm{k}}$ is :