$\vec u = 1,1,-1$ and $\vec v = 1,1,1$
So, $\vec p$ is projection vector $\vec u$ into $\vec v$ and $\vec q$ is the projection vector $\vec v$ into $\vec u$
$\cos \theta = 1/3$
I have tried but the answer i got is $\frac 92$ the right answer is $\frac 92 \sqrt 2$
How to do cross product to find the area of parallelogram?
Cross product like this https://www.analyzemath.com/stepbystep_mathworksheets/vectors/cross_product.html