\(1)A\left(x\right)=6x^4-5x^2+4x-3x^4+2x^3\\ =\left(6x^4-3x^4\right)+2x^3-5x^2+4x\\ =3x^4+2x^3-5x^2+4x\\ 2)A\left(x\right)=x^5+x^4-3x+7-2x^4-x^5\\ =\left(x^5-x^5\right)+\left(x^4-2x^4\right)-3x+7\\ =-x^4-3x+7\\ 3)A\left(x\right)=3x^2-2x+7+2x-3x^2-6\\ =\left(3x^2-3x^2\right)+\left(-2x+2x\right)+\left(7-6\right)\\ =1\)
\(4)A\left(x\right)=3x^2+7x^3-3x^3+6x^3-3x^2\\ =\left(7x^3+6x^3-3x^3\right)+\left(3x^2-3x^2\right)\\ =10x^3\\ 5)A\left(x\right)=1-6x^7+5x^4-2+13x^5-8x^7\\ =\left(-6x^7-8x^7\right)+13x^5+5x^4+\left(1-2\right)\\ =-14x^7+13x^5+5x^4-1\\ 6)A\left(x\right)=2-9x^2+4x^5-3x^3+x-4x^5\\ =\left(4x^5-4x^5\right)-3x^3-9x^2+x+2\\ =-3x^3-9x^2+x+2\)