Factorise the following:-

$4x^2-y^2-3xy+2x-2y$

Factorise the following:-

Factorise the following:-

$a^4+b^4-7a^2{b}^2$

Factorise the following:-

$x^4-14x^2+1$

Express each of the following as the difference of two squares:-

Express each of the following as the difference of two squares:-

Express each of the following as the difference of two squares:-

$(x^2+5x-7)(x^2-5x+7)$

Evaluate the following by using factors:-

$(979{)}^2-(21{)}^2$