Bài 1:
\(f\left(x\right)+g\left(x\right)=6x^4-3x^2-5\)
\(f\left(x\right)-g\left(x\right)=4x^4-6x^3+7x^2+8x-9\)
Do đó: \(2\cdot f\left(x\right)=10x^4-6x^3+4x^2+8x-14\)
=>\(f\left(x\right)=5x^4-3x^3+2x^2+4x-7\)
\(g\left(x\right)=5x^4-3x^3+2x^2+4x-7-4x^4+6x^3-7x^2-8x+9\)
\(=x^4+3x^3-5x^2-4x+2\)