（a-1分之1-2a+a²)-(a²-a分之√a²-2a+1),
=（a-1）²/（a-1）-√（a-1）²/a(a-1)
=a-1-(a-1)/a(a-1)
=a-1-1/a
=1/(2+√3)-1-(2+√3)
=(2-√3)/(4-3)-3-√3
=2-√3-3-√3
=-1-2√3
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