a: P(x)=-3x^2+6x-2
Q(x)=5x^4+4x^3+9x^2-6x-12
b: \(P\left(x\right)+Q\left(x\right)\)
\(=-3x^2+6x-2+5x^4+4x^3+9x^2-6x-12\)
\(=5x^4+4x^3+6x^2-14\)
\(P\left(x\right)-Q\left(x\right)\)
\(=-3x^2+6x-2-5x^4-4x^3-9x^2+6x+12\)
\(=-5x^4-4x^3-12x^2+12x+10\)
c: Q(x)-P(x)
=-(P(x)-Q(x))
\(=5x^4+4x^3+12x^2-12x-10\)