13.a)(2x)·(3y)·(-xy)=6xy·(-xy)=-6x²y²b)(2x²y)·(-1/3x)·(-6xy²)=(-2/3·x³y)·(-6xy²)=12/3·x⁴y³=4x⁴y³
c)√ab)·(√3a²b)·(-√6ab²)=√(3a³b²)·(-b√6a)=ab√(3a)·(-b√6a)=-ab²√(18a²)=-3a²b²√2
d)(2/3xa²)·(3/4x²a)·(-2y)=(2xa²/3)(3x²a/4)(-2y)=6x³a³/12·(-2y)=-12x³ya³/12=-x³ya³