A vector \( \vec{a} \) is parallel to the line of intersection of the plane determined by the vectors \( \hat{\imath}, \ \hat{\imath}+\hat{\jmath} \) and the plane determined by the vectors \( \hat{\imath}-\hat{\jmath}, \ \hat{\imath}+\hat{k} \). The obtuse angle between \( \vec{a} \) and the vector \( \vec{b}=\hat{\imath}-2\hat{\jmath}+2\hat{k} \) is:
