The sum of two vectors \(\rm \vec b\) and \(\rm \vec c\) is a vector \(\rm \vec a\) such that \(\rm \left|\vec a \right|=\left|\vec b \right|=\left|\vec c \right|=4\). Then, find the angle between \(\rm \vec b\) and \(\rm \vec c\).
1
160°
2
120°
3
60°
4
135°