If `vec(a)` and `vec(B)` are two vectors such that `|vec(a)|=|vec(b)|=sqrt(2)` and `vec(a).vec(b)=-1`, find the angle between `vec(a)` and `vec(b)`.

Explanation

Let `theta` be the angle between `vec(a)` and `vec(b)=-1`
`hArr |vec(a)|.|vec(b)|. cos theta=-1 hArr sqrt(2)xxsqrt(2)xx cos theta=-1`
`hArr cos theta=(-1)/2 hArr theta = (2pi)/3" "[ :' 0 le theta le 2pi]`.
Hence, the angle between `vec(a)` and `vec(b)` is `(2pi)/3`.