什么叫卷，什么叫忙？

看下面这道题：

9-4
=3²-2²
=(3+2)(3-2)
=[(√3+√2)2-2√6](√3-√2)(√+√2)
=[(3+2√6+2)-2√6](√3-√2)(√3+√2)
=(3+2√6+2-2√6)(√3-√2)(√3+√2)
=5(√3-√2)(√3+√2)
=(5√3-5√2)(√3+√2)
=5√3√3+5√3√2-5√2√3-5√2√2
=15+30-30-10
=45-40
=5