6a²(a-5)-(a-5)³
21a²b-4b-12a+7ab²
разложить на множители

6a²(a-5)-(a-5)³=(a-5)(6a²-(a-5)²)=(a-5)(6a²-a²+10a-25)=(a-5)(5a²+10a-25)=
5(a-5)(a²+2a-5)
21a²b-4b-12a+7ab²=7ab(3a+b)-4(b+3a)=(3a+b)(7ab-4)