(y-4)(y+4)-(y-3)^2=(y^2-16-(y^2-6y+9))=y^2-16-y^2+6y-9=6y-25
(a+2)-(a+3)^2=(a+2-(a^2+6y+9))=a+2-a^2-6y-9=-(a^2+7+5y)
(y-4)(y+4)-(y-3)^2=(y^2-16-(y^2-6y+9))=y^2-16-y^2+6y-9=6y-25
(a+2)-(a+3)^2=(a+2-(a^2+6y+9))=a+2-a^2-6y-9=-(a^2+7+5y)