引用:
Originally posted by 戀櫻 at 2006-1-10 12:58:
我叫你教我，並唔係要answers
答案我都有la
我要step呀!
I already show you SBS on your question #2
Here is the #1. First, expand your original question
r^2+(s-a)r-as=r^2+rs-ra-as
Draw a little "diagram" as follow
r a
X
r s
First colume, rxr=r^2 satisfied what your original question and so does second colume a x s = as except plus instead of minus in the question, so we know there must be one of them should be "negative", only have to find out which one. We can determine in the next step. Now multiply across. which are r x s and r x a. In the expanded question, ra is "minus" But rxr is positive. So we know "a" must be minus in order to get "-ra" (Cannot be "r" because if "r" x "-r" = "-r^2"
and also (-a)xs=-sa which is satisfied the requirement on your original question. Therefore the little diagram should be like this
r -a
X
r s
and there you go, there is your answer (r-a)(r+s). Hope this explains
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Last edited by WTF on 2006-1-10 at 18:40 ]
