(x+2)/(x-3)除以(x+1)/(x-2)
=(x+2)/(x-3)*[(x-2)/(x+1)]
=(x+2)(x-2)/[(x-3)(x+1)]
使得代数式有意义的x满足：
x-3≠0且x-2≠0且x+1≠0
即：x≠3且x≠2且x≠-1