(5x四次方-10x三次方y+25x平方y平方)÷(-5x平方)
=[5x^4-(10x^3)y+25(x^2)(y^2)]÷(-5x^2)
=(5x^2)(x^2-2xy+5y^2)÷(-5x^2)
=-(x^2-2xy+5y^2)
=2xy-x^2-5y^2