a: \(P\left(x\right)=x^5+7x^4-9x^3-2x^2-\dfrac{1}{2}x\)
\(Q\left(x\right)-x^5+5x^4-2x^3+4x^2-\dfrac{1}{4}\)
b: \(P\left(x\right)+Q\left(x\right)=12x^4-11x^3+2x^2-\dfrac{1}{2}x-\dfrac{1}{4}\)
\(P\left(x\right)-Q\left(x\right)=2x^5+2x^4-7x^3-6x^2-\dfrac{1}{2}x+\dfrac{1}{4}\)