27.2
а) (x-5)(9-x)=9x-x²-45+5x=-x²+14x-45
б) (-8-a)(b+2)=-8b-16-ab-2a=-ab-2a-8b-16
в) (y-10)(-y+6)=-y²+6y+10y-16=-y²+16y-16
г) (-7-b)(a-4)=-7a+28-ab+4b=-ab-7a+4b+28
27.2
а) (x-5)(9-x)=9x-x²-45+5x=-x²+14x-45
б) (-8-a)(b+2)=-8b-16-ab-2a=-ab-2a-8b-16
в) (y-10)(-y+6)=-y²+6y+10y-16=-y²+16y-16
г) (-7-b)(a-4)=-7a+28-ab+4b=-ab-7a+4b+28