1)4a^2-12ab+5b^2 = (2a-3b)^2-4b^2=(2a-3b-2b)(2a-3b+2b)=
=(2a-5b)(2a-b);
2)9c^2-24cd+7d^2=(3x-4d)^2-9d^2=(3c-4d-3d)(3c-4d+3d)=
=(3c-7d)(3c-d);
3)25a^2-20ab-12b^2=(5a-2b)^2-16b^2=(5a-2b-4b)(5a-2b+4b)=
=(5a-6b)(5a+2b);
4)9m^2-30mk+16k^2=(3m-5k)^2-9k^2=(3m-5k-3k)(3m-5k+3k)=
=(3m-8k)(3m-2k).