Therefore, when a=3 or a=-3, the score is meaningless.
2. To put it simply, since I said that x/y=2, I will assume that x=2, y= 1, and substitute the available answer =3 (this kind of fill-in-the-blank question or multiple-choice question can be calculated like this, which is fast and time-saving).
3.[( 1+4)/(a？ -4)]×[(a+2)/a]= [a？ /(a？ -4)] [ (a+2)/a ] =a？ (a+2)/[(a+2)(a-2)a]=a/(a-2), and a≠0, a≠2, a≠-2,
4.(x？ -9)/(x？ -3x) = (x+3) (x-3)/[x (x-3)] = (x+3)/x =1+3/x, and x≠3, x≠0.