1) (x-3)(x-7)-2x(3x-5)=x²-7x-3x+21-6x²+10x=21-7x²=7(3-x²)
2) 2(m+1)²-4m=2(m²+2m+1)-4m=2m²+4m+2-4m=2m²+2=2(m²+1)
3) 4a(a-2)-(a-4)²=4a²-8a-(a²-8a+16)=4a²-8a-a²+8a-16=3a²-16
1) x³-9x=x(x²-9)=x(x-3)(x+3)
2) -5a²-10ab-5b²=-(5a²+10ab+5b²)=-5(a²+2ab+b²)=-5(a+b)²