Factorise:

$7(x-2 y)^{2}-25(x-2 y)+12=7(x-2 y)^{2}-21(x-2 y)-4(x-2 y)+12$

$=[7(x-2 y)](x-2 y-3)-4(x-2 y-3)$

$=[7(x-2 y)-4](x-2 y-3)$

$=(7 x-14 y-4)(x-2 y-3)$

Hence, factorisation of $7(x-2 y)^{2}-25(x-2 y)+12$ is $(7 x-14 y-4)(x-2 y-3)$.