Verified answer

3.

а) (x-3)(x-7)-2x(3x-5)=x²-3x-7x+21-6x²+10x=-5x²+21

б) 4a(a-2)-(a-4)²=4a²-8a-(a²-8a+16)=4a²-8a-a²+8a-16=3a²-16

в)2(b+1)²-4b=2(b²+2b+1)-4b=2b²+4b+2-4b=2b²+2

4.

a²-b²=(a-b)(a+b)

a)16x⁴-81=(4x²)-9²=(4x²-9)(4x²+9)=(2x-3)(2x+3)(4x²+9)

б)x³-9x=x(x²-9)=x(x-3)(x+3)

в) -5a²-10ab-5b²=-5(a²+2ab+b²)=-5(a+b)²