B1:
a) \(x^2\left(x+2\right)-3x\left(x^2-1\right)\)
= \(x^3+2x^2-3x^3+3x=-2x^3+2x^2+3x\)
b) \(x^3\left(x-4\right)+\left(x^2+3\right)\left(-x\right)-x^4\)
= \(x^4-4x^3-x^3-3x-x^4=-5x^3-3x\)
B2:
a) \(2x\left(x-5\right)-x\left(3+2x\right)=26\)
\(2x^2-10x-3x-2x^2-26=0\)
\(-13x-26=0\)
\(-13\left(x+2\right)=0\)
\(\Rightarrow x+2=0\Rightarrow x=-2\)
b) \(x\left(x^2+x+1\right)-x^2\left(x+1\right)-x+5=4\)
\(x^3+x^2+x-x^2-x^3-x^2-x+5-4=0\)
\(-x^2+1=0\Rightarrow-x^2=-1\Rightarrow x=\pm1\)
\(x^2\left(x+2\right)-3x\left(x^2-1\right)\)
\(=x^3+2x^2-3x^3-3x\)
\(=-2x^3+2x^2-3x\)
\(x^3\left(x-4\right)+\left(x^2+3\right)\left(-x\right)-x^4\)
\(=x^4-4x^3+-x^3-3x-x^4\)
\(=-5x^3-3x\)
