x^3y^3+x^2y^2-4xy-64
=(x^3y^3-64)+(x^2y^2-4xy)
=(x^3y^3-4^3)+xy(xy-4)
=(xy-4)(x^2y^2+4xy+16)+xy(xy-4)
=(xy-4)(x^2y^2+4xy+16+xy)
=(xy-4)(x^2y^2+5xy+16)
提示:运用立方差公式后提取公因式