1.写出一个一元二次不等式,使它的解集为（2-根号3,2+根号3）2.已知X,Y∈R,比较x^2+y^2与2(2x-y)-5大小

(x-2-√3)(x-2+√3)(x-2)^2-3x^2-4x+4-3x^2-4x+1x^2+y^2-[2(2x-y)-5]
=x^2+y^2-[4x-2y-5]
=x^2+y^2-4x+2y+5
=x^2-4x+4+y^2+2y+1
=(x-2)^2+(y+1)^2
因为(x-2)^2>=0,(y+1)^2>=0
所以(x-2)^2+(y+1)^2>=0
即x^2+y^2>=2(2x-y)-5

1.
(x - (2-√3) ) ( x - (2+√3) ) =0
x^2 -4x - 1 = 0
2.
x^2+y^2 - (2(2x-y)-5 )
=(x^2 -4x + 4) + (y^2 + 2y + 1)
= ( x-2)^2 + (y+1)^2 ≥ 0
x^2+y^2 ≥ 2(2x-y)-5

1.
x^2-4x+1