1)
x=-1/3
-3x^2-10x-3=-3*(-1/3)^2-10*(-1/3)-3=-1/3+10/3-3=0
2)
-2a+4a^2-a^3+a-a^2+2=-a^3+3a^2-a+2
5x^3*(-3y^2)-2x^2y*8x+6x^2y^2*3x=-15x^3*y^2-16x^3y+18x^3y^2=
=3x^3*y^2-16x^3y
3)
-x^2+2xy-2y^2
4x^2+2xy+2y^2
(-x^2+2xy-2y^2) + (4x^2+2xy+2y^2) = 3x^2+4xy
(-x^2+2xy-2y^2) - (4x^2+2xy+2y^2) = -5x^2-4y^2