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My simple math problems

  1. Sep 10, 2009 #1
    So I've been having some trouble doing well on my math quizzes and exams, and it's gotten to the point where I feel I need to check everything I do because it's like everything is turning out wrong. Maybe I'm stressed or just psyched out, but I realize what it is that is hurting my performance and it isn't remembering the concepts, it's doing simple arithmetic.

    For example:

    Find a linear equation where f(1)=-2 and f(5)=6

    the right answer was y=2x-4, which was derived using the "find-the-linear-equation-formula" or y-y1=m(x-x1) and the slope formula. Very basic...very easy to do.

    I found the slope easily:


    so the equation became: y=2x+b

    Then for the bigger formula: I plugged in the numbers, so far so good,


    This is where everything went down hill. I forgot to distribute the 2 on the "x" side to the 5, so the equation looked like this:


    I then added 6 to the five to isolate the "y" and I had y=2x+1. Now most of you probably think "hey, that was pretty stupid", well fortunately I discovered this problem in time to fix it and get the right answer, only to realize that the other two problems on the quiz had similar mistakes, I mixed up domain with range on the first problem and didn't distribute the implied "-1" in [f(b+h)-f(b)]/h. So I thought about it and realize that simple stuff like this has been quite a hindrance on my grades, and probably the main reason I don't do very well on a lot of math, just simple arithmetic stuff like this...occasionally I'll make regular math mistakes, but this arithmetic thing is really killing me. I read somewhere that this is one of the more common mistakes is that people just don't see this stuff because of sloppy handwriting, maybe I might also be going too fast, I'm going to experiment with working on these two things, but maybe there might be something else I should be working on. So if anyone has ever had this problem and overcome it will you please tell me how you did it, and if it was the way I heard about, then please tell me, it'd help a lot.

  2. jcsd
  3. Sep 10, 2009 #2


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    Once you get to that point, don't overcomplicate things. You know that when you plug in x = 1, y = -2. So: -2 = 2*1 + b. It follows easily that b = -4. Or you can plug in the other number: x = 5, y = 6 gives: 6 = 2*5 + b, again you find b = -4.
    That's all there is to it.
  4. Sep 12, 2009 #3
    I've a tendency to make errors like this. Doesbn't everyone? I think it's a combination of tiredness, boredom and going to fast! You obviously know how to distribute 2(x-5). You've done a hundred problems like this and it's so basic you are just bored with having to do it again. So you start thinking about the film later tonight. So if you are rushing against time and daydreaming it's easy to get 2x - 5! The solution is simple though - always check the answer! But you seem to have, now, found that out for yourself. So where's the problem? You seem to be asking for a way to always get the right answer first time. Sorry can't be done. "To err is human...."
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