Is there any easy method to find cube and cuberoot??

Answer 1

well a cube is a number raised to the 3rd power. Cube roots are not usually easy to find, If you can use a calcuator its easier. Two ways, graph the function and the answers are when the graph crosses zero, or there is a solver function in the calcuator.

Answer 2

Actually, there is a method to find the cube of any number in one's head, but it is so simple that most people overlook it. However, be forewarned that it works best with relatively small numbers, because large ones make the mental work rather unmanageable. Can you imagine trying to cube a number like 312 in your head? Getting back to the subject at hand, all the method involves is the use of a binomial raised to the third power. That's right, those pesky little binomials we all played with in algebra and other courses actually can have a practical purpose. We just have to wake up and smell the roses, or rather, the binomials, as it were.

While calculating the cube of a number, it helps to be able to recall Pascal's Triangle. It also helps to be good at mental imaging and to have the ability to retain numbers in one's head for more than a fraction of a minute.

Recall that, by Pascal's Triangle,
(a+b)^3 = a^3 + (3a^2)(b) + (3a)(b^2) + b^3.

Now suppose we wanted to cube some poor unsuspecting number, like 11, for example. 11 is simply 10 + 1, so we could plug those numbers directly into a binomial cubed and crank out the answer in our head.

(11)^3
= (10 + 1)^3
= (10)^3 + 3[(10)^2](1) + 3(10)(1)^2 + (1)^3
= 1000 + 300 + 30 + 1
= 1331

Now, that wasn't too bad, was it? We found the cube of a number and survived to tell the tale. Just remember, in order to get good at this, it requires some practice. So, next time you want to do so, just walk up to the nearest person and ask them to give you any number from 1 to 100 to cube, and just watch as their jaw hits the floor. By the way, this method also works for squaring a number: (a + b)^2 = a^2 +2ab + b^2.

As for the method for finding the cube root of a number, 'bequalming' was right on with his recommendation of the website he cited.

Answer 3

You mean without using a calculator? The best way to find cubes is to actually carry out the operation. It's cube roots that are more difficult to find. The most efficient way for many cube roots (if they aren't huge) is to use Newton's method:

To find cube root of a, solve the equation f(x) = x^3 - a = 0 using Newton's method:

choose x[0]
x[n+1] = x[n] - f(x[n])/f'(x[n])

repeat until answer doesn't change any more. f'(x[n]) represents the derivative of f, which is 3x[n]^2.

Answer 4

Finding cube roots is tedious enough to where i'd say the best way to do it by hand is with logarithms. In other words, get the logarithm of the number from a logarithm table, divide the logarithm by 3 (since you want x^(1/3) ), and look up the number you just calculated.

If you haven't learned about logarithms yet, then I'm afraid you're stuck with one of the interpolation methods, as described by some of the other posters.

Answer 5

To find the cube, multiply the numbers out. To find the cube root, check the link below (and some related pages on the site)

Answer 6

Doing cube roots by hand is now a lost art (as well it should be!), but you may find it fun to try. Here is a link that shows the method that I learned to use when I was in high school. BTW, don't ask how old I am, you will think I am ancient! :)

http://mathforum.org/library/drmath/view/52605.html

HTH

Charles

Answer 7

for cube just multiply it out. thats the only way. for cube root you can raise it to the 1/3 power because of the radical / exponent rules so (cubed root)x = x^(1/3)