√3+1/√3-1
=（√3+1）（√3+1）/2
=（3+2√3+1）/2
=√3+2
1＜√3＜2
a=3
b=√3+2-3=√3-1
a²+3ab+b²
=（a+b）²+ab
=（√3+2）²+3√3-3
=3+4+4√3+3√3-3
=7√3+4