\(a,2x\left(4x^2-5\right)\)
\(=8x^3-10x\)
\(b,3x^2\left(2y-1\right)-\left[2x^2\left(5y-3\right)-2x\left(3x^2+1\right)\right]\)
\(=6x^2y-3x^2-\left[10x^2y-6x^2-6x^3-2x\right]\)
\(=6x^2y-3x^2-10x^2y+6x^2+6x^3+2x\)
\(=-\left(10x^2y-6x^2y\right)+\left(6x^2-3x^2\right)+6x^3+2x\)
\(=-4x^2y+3x^2+6x^3+2x\)