Determine the area of parallelogram whose adjacent sides are the vector `hati+hatj, -hati+2hatj`

Explanation

Let `veca = hati+hatj, vecb = -hati+2hatj`
Then `vecaxxvecb = (hati+hatj)xx(-hati+2hatj)`
=`-hatixxhati+2hatixxhatj-hatjxxhati+2hatixxhatj`
`2hatk+hatk = 3hatk`
Area of the parallelogram
=`|vecaxxveca| = |3hatk|` = 3 square units.