(5x^-2/3 y^1/2)(-1/4x^-1 y^1/2)(-5/6x^1/3 y^-1/6)
=（5x1/4x5/6）x^(-2/3-1+1/3) y^(1/2+1/2-1/6)
=25/24 x^-4/3 y^5/6