I'm doing some algebraic mistake because I think my method is right.

The question is to find the gradient of $\displaystyle (p+q-1, q+p-3)(p-q+1, q-p+3)$

My attempt for the question is.

$\displaystyle \frac{(q-p+3)-(q+p-3)}{(p-q+1)-(p+q-1)}$

$\displaystyle \frac{q-p+3-q-p+3}{p-q+1-p-q+1}$

$\displaystyle \frac{-2p+6}{-2q+2}$

$\displaystyle \frac{2p+3}{2q+1}$

$\displaystyle ans = \frac{p+3}{q}$

But the answer on the book is different.