\(1)2xy^3x\left(x^3y-2xy^3+4\right)\)
\(=2xy^3x.x^3y-2xy^3x.\left(-2xy^3\right)+2xy^3x.4\)
\(=2x^5y^4+4x^3y^6+8x^2y^3\)
\(2)-\dfrac{1}{3}a^2b\left(-3ab^2+6b-9a\right)\)
\(=-\dfrac{1}{3}a^2b.\left(-3ab^2\right)-\dfrac{1}{3}a^2b.6b+\dfrac{1}{3}a^2b.9a\)
\(=a^3b^3-2a^2b^2+3a^3b\)