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If your calculator only does square roots, try this to get approximate 
cube roots:

    1. Take the number you want to find the cube root of, and square 
       root it twice.

    2. Multiply the result of step 1. with the the number you want to 
       find the cube root of.

    3. Square root the result of step 2.  Write it down.

    4. Square root the result of step 3.  Write it down.

    5. Divide the number you want to find the cube root of by the 
       number you got in step 3.

    6. Subtract the number you got in step 4 from the number you got 
       in step 5.

    7. Divide the result of step 6 by 3.

    8. Add the result of step 7 to the number you got in step 4.  
       This is the answer.

For example, to find the (approximate) cube root of 10:

  Step  Operations            Result
  ----  --------------------- ---------------
    1.  Sqrt(Sqrt(10))        = 1.7782794
    2.  1.7782794 * 10        = 17.782794
    3.  Sqrt(17.782794)       = 4.216965  <== Write it down!
    4.  Sqrt(4.216965)        = 2.053525  <== Write it down!
    5.  10 / 4.216965         = 2.371374
    6.  2.371374 - 2.053525   = 0.31784872
    7.  0.31784872 / 3        = 0.10594957
    8.  0.10594957 + 2.053525 = 2.1594746 <== The answer!

  Check the answer: 2.1594746 * 2.1594746 * 2.1594746 = 10.07034386991
  (Actual answer is 2.1544347.)
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