a.
\(3x^2\left(2x^3-x+5\right)=6x^5-3x^3+15x^2\)
\(\Rightarrow6x^5-3x^3+15x^2=6x^5-3x^3+15x^2\)
\(=6x^5-3x^2+15x^2-6x^5-3x^3+15x^2\)
= 0
b.
\(\left(4xy+3y-5x\right)x^2y=4x^3y^2+3x^2y^2-5x^3y\)
\(\Rightarrow4x^3y^2+3x^2y^2-5x^3y=4x^3y^2+3x^2y^2-5x^3y\)
= 0