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Simple math .just not for me

  1. Jul 14, 2009 #1
    simple math.....just not for me

    I'm currently in Mechanics of Materials and I have reduced my problem to something similar to: 510/7.6=8.25/((pi/4)*d^2)

    how do I solve for d? I have been given the answer (from the back of the book) but i don't remember how to solve for d......by the way the above numbers are random and not from my text.....but it is similar...thx crich
     
  2. jcsd
  3. Jul 14, 2009 #2
    Re: simple math.....just not for me

    There are a couple possible first-steps to take.

    1. Take the reciprocal of both sides.

    2. Multiply both sides by d^2

    Either way, your main strategy should be getting d^2 by itself.
     
  4. Jul 14, 2009 #3
    Re: simple math.....just not for me

    so I would have :
    ((pi/4)*510)/(8.25*7.6)=1/d^2 ......?
     
  5. Jul 14, 2009 #4

    Mark44

    Staff: Mentor

    Re: simple math.....just not for me

    No. The goal is to get d2 all by itself on one side.
    Here's where you're starting from:
    [tex]\frac{510}{7.6} = \frac{8.25}{(\pi/4) d^2}[/tex]

    The simplest thing to do is to take the reciprocals of both sides, as pinu7 suggested (the idea is that, if a/b = c/d, then b/a = d/c).

    After that, it should be a relatively simple matter to isolate the d2 factor. The final step would be taking the square root of both sides, keeping in mind that d can have two values: one positive and one negative.
     
  6. Jul 14, 2009 #5
    Re: simple math.....just not for me

    okay so I would have sqr((8.25*7.6)/((PI/4))*510)=d
     
  7. Jul 14, 2009 #6

    Mark44

    Staff: Mentor

    Re: simple math.....just not for me

    Yes, but again there are mathematically two possible values for d, although the negative value might not be relevant for your problem.
     
  8. Jul 14, 2009 #7
    Re: simple math.....just not for me

    Okay...thx the ans is going to be postive b/c it is a force...thx for all yall's help
     
  9. Jul 14, 2009 #8
    Re: simple math.....just not for me

    okay so I'm home now and I've tried what was suggested but, I still don't get the right ans...:
    510/1.75=8.30/(pi/4)*d^2

    I used the reciprocals and got 1.75/510=(pi/4)*d^2/8.30 ... reduced and I got
    sqr root (4*8.30*1.75/pi510)=d ans:.5982 the book ans is 6.02.... where did I go wrong?
     
  10. Jul 14, 2009 #9
    Re: simple math.....just not for me

    nevermind I got it.... I didn't make all the units match
     
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