Question 8099: I am having a problem with "special cases of factoring".
x^2-100
I think that it is, (x+100)(x-100)
Answer by prince_abubu(198)   (Show Source):
You can put this solution on YOUR website! I don't think you're having that big of a problem with this. Actually, it's (x+10)(x-10). If you do the FOIL on the (x+10)(x-10), you'll get  .
You're probably having a problem, perhaps in recognizing what some special cases might look like. The above example you showed is known as "difference of squares". The way to recognize that is if you've got an expression of the form  , and I stress MINUS, otherwise, it won't work. In this case BOTH  and  have to be perfect square numbers so that you can write it as (ax + b)(ax - b).
For example,  is a difference of squares BECAUSE the 25 and the 9 are both perfect square numbers, there are ONLY two terms where one is in  and the other, a constant, and there's that minus sign in between. In that case, that can be guaranteed to be written as (5x + 9)(5x - 9).
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