1. а) (х+5)²-5х(2-х) = x²+10x+25-10x-5x²= -4x²+25
б) 16у+2(у-4)²=16y+2(y²-8y+16)=16y+2y²-16y+32=2y²+32
2. a) 81-а²=(9-a)(9+a)
б) 5х²-5у²=5(x²-y²)=5(x-y)(x+y)
в) 3х²-6ху+3у²=3(x²-2xy+y²)=3(x-y)²
3. (a²+4а)²-а²(а-2)(а+2)-4а²(2а-1)= a⁴+8a³+16a²-a⁴+4a²-8a³+4a²= 20a²