已知x=根号3+根号2,y=根号3-根号2,求2x^2-xy-2y^2
问题描述：
已知x=根号3+根号2,y=根号3-根号2,求2x^2-xy-2y^2
答
x=根号3+根号2,
y=根号3-根号2
xy=1, x+y=2√3,x-y=2√2
2x^2-xy-2y^2
=2（x+y)(x-y)-xy
=2*2√3*2√2-1
=8√6-1