2 2/3*x^5*y^8*(-1 1/2*x^3*y^6)^2
2 2/3*x^5*y^8*(-1 1/2x³*y^6)²=
=8/3*x^5y^8*(-3/2 *x³*y^6)²=
=8/3*x^5y^8*(9/4x^6y^12)=
=72/12x^11y^20=
=6x^11y^20