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| Raising a number to a non-integer power. |
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| Circlotron:
Okay, so 4^3 = 4x4x4 = 64. But 4^3.9 = ?? = 222.861. How can you multiply a number by itself a non-integer amount of times? |
| greenpossum:
It's just the extension in the real number domain of taking the exponent. Mathematics is like that, analogies can only go so far. But if you like, think of it as 4^(39/10) so take the 39th power of 4 and then the 10th root. Things get tricky to imagine when the exponent is irrational. |
| Ian.M:
I'm no mathematician so the terminology here is going to give a real mathematician fits. Without getting into logarithms, or huge powers of four, break that down to: 43 x root10(4)9 root10(n) is the tenth root of n, i.e, the function where if: m=root10(n) then: m10=n That approach is valid for any rational real number. As GreenPossum points out, its not any help with irrational numbers. so letting X be the exponent, although it gives you a function with an infinite number of points along any interval of the X axis, it isn't continuous. To get the 'in-between' irrational values you have to consider exponentiation as multiplying the logarithm of n by the power X, then taking the antilog, which works in any base of logarithms, and is a continuous function, numerically identical to the 'classic' multiplying numbers by them-selves X times concept for any real rational X. Where it gets gnarly to conceptualise is when you start extending exponentiation YX into the complex number domain for both Y and X. I cant wrap my brain around the number of dimensions required to visualise that plot - its bad enough visualising the complex result of a function operating on a single real number parameter, which is a 3D plot. |
| RoGeorge:
--- Quote from: Circlotron on May 27, 2020, 06:00:11 am ---Okay, so 4^3 = 4x4x4 = 64. But 4^3.9 = ?? = 222.861. How can you multiply a number by itself a non-integer amount of times? --- End quote --- Short answer, the exponential function is defined as a polynomial. Explanation starts at minute 7:00, at about 7:50 is exactly your question. |
| tom66:
--- Quote from: Circlotron on May 27, 2020, 06:00:11 am ---Okay, so 4^3 = 4x4x4 = 64. But 4^3.9 = ?? = 222.861. How can you multiply a number by itself a non-integer amount of times? --- End quote --- Because log10(222.861)/log10(3.9) = ~4. And that is the division of two base10 logarithms. You can easily define log10(n), and you have inferred what the solution to your non-integer power is with nothing more than division. Mathematical operations often have an inverse. Try fractional and negative factorial if you -really- want to blow your mind. |
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