Wednesday, June 9, 2010

How to Take the Cube Root on a Calculator without a Cube Root Key

Need to take the cube root of a number on a scientific calculator without a cube root key? No problem! Need to take a fourth root, a fifth root, a fourth root of the number cubed? Not a problem either!

How to Take a Cube Root:

1. Start by taking the Logarithm of the number. For example, if you were using a TI-35 calculator and the number you wanted to take the cube root of was 4, you would type 4 and then hit the “ln” key. The result for the number 4 would be about 1.386. Write this number down on a sheet of paper if necessary.

2. Divide the number found in step 1 by 3. In our example, the result would be 1.386/3 = 0.462

3. Now, take the “inverse log” of the number from step 2. This is marked by a small “e” symbol with a superscript “x” above it, written directly above the “ln” key. To access this key, press the “Inv” key (located in the middle of the calculator) and then “ln” key. If you did this step right, for our example, the number that you get should be 1.587.

4. If your calculator doesn’t have an “Inv” key, try the shift key instead. Hint: usually the key will have the same color of letters as the letters that the “e” with a superscript “x” are written in.

Finding other roots:

5. You can also calculate a fourth, fifth, sixth, etc. root using this technique. For a fourth root, you repeat all of the steps above with the exception that you divide by 4 in step 2. For a fifth root, you would divide by 5.

6. If you want to take a complex root, say the forth root of 4 cubed, you would repeat all of the same steps as above, only you would multiply by 3/4 in step 2. Want to take the sixteenth root of 4 to the eight power? Change the fraction in step 2 to 8/16.

7. Remember to change the number in step 1 if you’re not finding the cube root, etc. of 4. For example, if you’re finding the cube root of 5, change the number in step 1 to 5 and follow the rest of the instructions.

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