If `vec(a) = 2hat(i) - 3hat(j) + hat(k), vec(b) = -hat(i) + hat(k)` and `vec(c) = 2hat(j) - hat(k)` are three vectors, then find the area of the parallelogram having diagonals `(vec(a) + vec(b))` and `(vec(b) + vec(c))`.

Answer

`(1)/(2) sqrt(21)` sq. units