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Making Obvious Mistakes

  1. May 23, 2012 #1
    While working through my Algebra II today, I managed to solve [itex] \sqrt [3] { \frac{27a}{4b^4}} [/itex], and yet... I had to ask for help in the homework section because I neglected to notice the difference between a square and a cube root.

    Anyone else do things like that? Please commiserate with me. :shy:
  2. jcsd
  3. May 23, 2012 #2


    Staff: Mentor

    I wouldn't worry about it too much, as long as you are now able to tell the difference between the two kinds of roots. A lot of mathematics is paying attention to details, a skill that requires training.
  4. May 23, 2012 #3
    I got a horribly low grade on a general chemistry 2 exam because I made a series of stupid mistakes.

    1) I didn't pay attention to see that the reactant in a reaction was a solid, so the equilibrium constant would NOT include the concentration of that species... because it's a solid.

    2) Forgot to convert joules to kilojoules

    3) Misread a question because I went too fast. He gave the E0 value of a reaction in one direction, so I said that was the cathode. However, in the combined reaction, it actually went in the opposite direction, so it was the anode.

    4) Randomly subtracted instead of added a number in a given equation where the number was clearly positive.

    These were all multiple choice questions, so no partial credit. Those 4 alone meant my maximum score would have been 80. Couple that with the ones I genuinely struggled with, and I ended up with a 65%. It was really embarrassing for a senior-year physics major to fail so hard on a freshman-level chem exam.
  5. May 23, 2012 #4
    How the heck did you solve that? It has variables in it.

    Sometimes when I take tests, I'll be sitting there, staring at the test, wondering why I can't figure out this problem, and then realize it's something obvious. Sometimes I stare at it so long, I'll memorize it and get it wrong on the test, but when I get home, I'll type it up exactly into Wolframalpha from memory, and see that it's such an obvious answer that I couldn't think of.
  6. May 24, 2012 #5
    @leroyjenkens: It was a given that each radical represents a real number. And technically, I should say "simplified" instead of "solved." I hope that clears it up.

    Phew! I'm glad I'm not the only one. Once I realized I did that yesterday, I just had to laugh at myself. Many people that know me point out that I often catch more complex things but miss the simple things. Math is one of those fun subjects that is always tripping me up because there are so many different ways to mess it up! So, it's constantly just making sure my arithmetic is correct as well as the actual algebra part.

    A couple weeks ago, I was puzzling over a different problem (I think it was just simplifying a polynomial), and I kept getting the wrong answer much to my dismay. And one of my family members just looks over my shoulder and within three seconds points out, "You missed the sign change there."

    Such is my life; I still have more radical work today, so wish me luck everyone! And I will gladly return the favor to you too!
  7. May 24, 2012 #6
    These problems happen, but are easily treated with a steady sleep and exercise schedule, healthy diet, and trips to the ophthalmologist.

    Additionally, look over your work before turning it in. Everyone wants to look impressive and turn their test in, first. Don't be that person—it's a reckless side effect of high testosterone cramping your brain.
  8. May 25, 2012 #7
    @Illuminerdi: That's all around good advice for anything. I hope to implement it not just for my schoolwork's sake, but for other areas of life too. Thanks. :D
  9. May 30, 2012 #8
    Oh, I do stuff like that all the time. I was doing an independent study with a professor over the winter, and I was constantly being tripped up by really stupid things, right in front of her. Examples: I decided 13x2=29 instead of 26, I couldn't remember how to complete the square, I somehow managed to forget that factoring a polynomial was not in fact the same as taking its square root (?!).
  10. May 31, 2012 #9
    I make dumb mistakes. So long as you understand the general concepts discussed, I wouldn't worry too much.
  11. Jun 16, 2012 #10
    @20Tauri: Ha ha! I completely understand that. Maybe, it's something like math stage fright??

    Thank you everyone for the reassurances. I was on vacation, so that is why it's been a while since you have heard from me. Now I'm back and ready to butt heads with my algebra quandaries once more. Good luck to all of you in all your math, chemistry, phsyics, etc. problems!
  12. Jun 16, 2012 #11
    It's been years and years since I've done any maths at all, and I've got a couple of months to get it just a bit up to scratch before it's back to the school bench.

    Only thing basically remember and could explain properly is simple division, multiplication, addition and subtraction. Only just starting getting the engines running getting back into how to do all those things in the hand when it comes to more complex stuff, and boy is my brain dusty.

    I was just doing some random divisions to get up to speed and one was 9347:17. Just random stuff. Anyway, it has a sequence of 16 decimals (forgive my possible lack of proper English math terms) or so and I kept getting it wrong untill I realised that several times around the 8th decimal I was suddenly dividing by 14 instead of 17. :biggrin:
  13. Jun 16, 2012 #12
    I don't think I've ever changed the divisor mid-problem, but what I usually do with division is I'll keep getting the wrong answer over and over and then suddenly realize that, for example, 45 divided by 5 is 9 and not 8. I'll keep getting 8 as the answer and can't figure out why I'm getting the question wrong. Weird. My brain isn't too good.
  14. Jun 20, 2012 #13
    I had to look up commiserate to see what it meant. Without knowing the meaning and thinking intuitively, I wasn't so sure if I wanted too. :smile:

    So that's what the 3 means! Cubed! :smile: Nearly for real, I've only just learned what that means. Seen it in my HS level AP text. Had to google it to see what it meant. Such clever symbolism.
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