a=(2+根号下3)分之1
=1×﹙2-√3﹚／[(2+√3﹚﹙2-√3﹚]
=2-√3
√﹙a²-2a+1)
=√﹙a-1)²
=√﹙2-√3-1)²
=√(1-√3﹚²
=√3-1