Given that the expression [tex]x^3+3x^2+x-5[/tex] represents the total length across the front of the mansion. Let the length of side I be a, then
[tex]x^4-2x^3+x-10+a-x^3+5x^2+2=x^3+3x^2+x-5 \\ \\ \Rightarrow a=x^3+3x^2+x-5-x^4+2x^3-x+10+x^3-5x^2-2 \\ \\ =\bold{-x^4+4x^3-2x^2+3}[/tex]
