a) \(\left(x-1\right)\left(x^5+x^4+x^3+x^2+x+1\right)\)
\(=x^6+x^5+x^4+x^3+x^2+x-x^5-x^4-x^3-x^2-x-1\)
\(=x^6-1\)
b) \(2\left(3x-1\right)\left(2x+5\right)-\left(4x-1\right)\left(3x-2\right)\)
\(=2\left(6x^2+13x-5\right)-\left(12x^2-11x+2\right)\)
\(=12x^2+26x-10-12x^2+11x-2\)
\(=37x-12\)