把x^2 y+x(y^2-2)-2y因式分解,并求当x=2+根号5,y=2-根号5时它的值

题目

把x^2 y+x(y^2-2)-2y因式分解,并求当x=2+根号5,y=2-根号5时它的值

答案

x^2y+x(y^2-2)-2y
=x²y+xy2-2x-2y
=xy(x+y)-2(x+y)
=(xy-2)(x+y)
=(-1-2)*4
=-12