1/2x^2-1/4x+0.2x^3+0.25x-0.5x^2-1/5x^3+0.5x-1
=(1/2x^2-0.5x^2)+(0.25x-1/4x)+(0.2x^3-1/5x^3)+0.5x-1
=0.5x-1
=0.5*12/13-13/13
=-7/13
1/2x^2-1/4x+0.2x^3+0.25x-0.5x^2-1/5x^3+0.5x-1
=(1/2x^2-0.5x^2)+(0.25x-1/4x)+(0.2x^3-1/5x^3)+0.5x-1
=0.5x-1
=0.5*12/13-13/13
=-7/13