a)\(A\left(x\right)=6x^2-5x+x^3-4x^2-7\\ =\left(6x^2-4x^2\right)-5x+x^3-7\\ =x^3-2x^2-5x-7\)
\(B\left(x\right)=-2x^2-5x+11+2x^2+x^3\\ =x^3+\left(-2x^2+2x^2\right)-5x+11\\ =x^3-5x+11\)
b)\(A\left(2\right)=x^3-2x^2-5x-7\\ 2^3-2.2^2-5.2-7\\ =8-8-10-7\\ =-17\)
\(B\left(-1\right)=x^3-5x+11\\ =\left(-1\right)^3-5.3+11\\ =\left(-1\right)-15+11\\ =-5\)
c)\(A\left(x\right)+B\left(x\right)=x^3-2x^2-5x-7+x^3-5x+11\\ =\left(x^3+x^3\right)+\left(-2x^2\right)+\left(-5x-5x\right)+\left(-7+11\right)\\ =2x^2+\left(-2x^2\right)+\left(-10x\right)+4\)
\(A\left(x\right)-B\left(x\right)=x^3-2x^2-5x-7-x^3+5x-11\\ =\left(x^3-x^3\right)+\left(-2x^2\right)+\left(-5x+5x\right)+\left(-7-11\right)\\ =\left(-2x^2\right)+\left(-18\right)\)
