1) = b^2 + 16b +64 - 4b^2 = - 3b^2 +16b+64
2) = ( y^2 + 2yb + b^2 ) ( y^2 - 2yb +b^2) = y^4 + y^3 ( - 2)b +y^2 b^2 + 2y^3 b - - 4y^2 b^2 + 2yb^3 + b^2 y^2 + b^3 ( - 2) y +b^4 = y^4+2y^2 b^2 - 4y^2 b^2 + b^4 = y^4 - 2y^2 b^2 + b^4 = - 2b^2 y^2 + y^4 +b^4
3) = x^2 + x ( - 1) y + yx +y^2 ( - 1) - x^2 - 3y^2= x ( - 1) y +yx - 4y^2=
= - xy+yx - 4y^2 = - 4y^2