正确答案：x⁴-7x²y²+81y⁴=x⁴+18x²y²+81y⁴-25x²y²=(x²+9y²)²-(5xy)²=(x²+9y²+5xy)(x²+9y²-5xy) 希望我的答案对你有所帮助！
x⁴-7x²y²+81y⁴=x⁴+18x²y²+81y⁴-25x²y²=(x²+9y²)²-(5xy)²=(x²+5xy+9y²)(x²-5xy+9y²)
