\(A\left(x\right)+B\left(x\right)=3x^4-4x^3+2x^2-3+8x^4+x^3-9x+\dfrac{2}{5}\)
\(=11x^4-3x^3+2x^2-9x-\dfrac{13}{5}\)
\(A\left(x\right)-B\left(x\right)=3x^4-4x^3+2x^2-3-8x^4-x^3+9x-\dfrac{2}{5}\)
\(=-5x^4-5x^3+2x^2+9x-\dfrac{17}{5}\)
\(B\left(x\right)-A\left(x\right)=8x^4+x^3-9x+\dfrac{2}{5}-3x^4+4x^3-2x^2+3\)
\(=5x^4+5x^3-2x^2-9x+\dfrac{17}{5}\)
\(A\left(x\right)+B\left(x\right)=11x^4-3x^3+2x^2-9x-\dfrac{13}{5}\)
\(A\left(x\right)-B\left(x\right)=-5x^4-5x^3+2x^2+9x-\dfrac{17}{5}\)
\(B\left(x\right)-A\left(x\right)=5x^4+5x^3-2x^2-9x+\dfrac{17}{5}\)