a2 + b2 - c2 - d2 + 2cd - 2ab
= (a2 - 2ab + b2) - (c2 -2cd + d2)
= (a-b)2 - (c-d)2
= (a-b+c-d)(a-b-c+d)
\(\left(a-b\right)^2-\left(c-d\right)^2=\left[\left(a-b\right)-\left(c-d\right)\right]\left[\left(a-b\right)+c-d\right]\)
\(\left(a+d-b-c\right)\left(a+c-b-d\right)\)