If a→,b→,c→ are three vectors such that a→+2b→+c→=0→ and a→=3,b→=4,c→=7 , find the angle between a ad b.

If $\vec{a}, \vec{b}, \vec{c}$ are three vectors such that $\vec{a} + 2 \vec{b} + \vec{c} = \vec{0}$ and $|\vec{a}| = 3, |\vec{b}| = 4, |\vec{c}| = 7$ , find the angle between a ad b.

Match the items on the right to the items on the left.