a: \(P\left(x\right)=x^5-3x^2+7x^4-9x^3+x^2-\frac14x\)
\(=x^5+7x^4-9x^3+\left(-3x^2+x^2\right)-\frac14x\)
\(=x^5+7x^4-9x^3-2x^2-\frac14x\)
\(Q\left(x\right)=5x^4-x^5+x^2-2x^3+3x^2-\frac14\)
\(=-x^5+5x^4-2x^3+3x^2+x^2-\frac14\)
\(=-x^5+5x^4-2x^3+4x^2-\frac14\)
b: P(x)+Q(x)
\(=x^5+7x^4-9x^3-2x^2-\frac14x-x^5+5x^4-2x^3+4x^2-\frac14\)
\(=12x^4-11x^3+2x^2-\frac14x-\frac14\)