[(-3xy)²·x³-2x² ·（3xy²）³ ·1/2y]÷9x⁴y²=【9x^5y^2-2x²*27x^3y^6*1/2y】÷9x⁴y²=【9x^5y^2-27x^5y^5】÷9x⁴y²=x-3xy^3