((-8)^2)^(1/3) <> (-8)^(2/3) <> (-8)^(1/3))^2

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In summary, the conversation discusses the validity of different equations involving cube roots and exponents. The first two equations give only real solutions, while the third equation gives a complex number. The reason for this is because the cube root of (-8) has three possible solutions, one real and two non-real. The first two equations only give the real solution, while the third equation gives one of the non-real solutions.
  • #1
nomadreid
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((-8)^2)^(1/3)=64^(1/3)=4
(-8)^(1/3))^2 = (-2)^2=4
but
(-8)^(2/3) = 4(-1)^(2/3) = 4((2/3)(cos (π) + i*sin(π)) and so forth, giving a complex number.
I understand why the latter one works. Why don't the first two?
Thanks.
 
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  • #2
nomadreid said:
((2/3)(cos (π) + i*sin(π))
Why does 2/3 act as a multiplicative constant instead of an exponential? Moreover ##\sin \pi =0##.
 
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  • #3
Your fifth equation isn't one.
 
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  • #4
Oops, too quickly typed the last equation. I meant to multiply the two-thirds times the angles, not times the whole expression (or equivalently use it as an exponent), using Euler's formula. Anyway, my question is not about Euler's formula, which as I say I do get when I am not typing while my bus is about to leave, but rather why the first two formulas are invalid.
 
  • #5
nomadreid said:
((-8)^2)^(1/3)=64^(1/3)=4
(-8)^(1/3))^2 = (-2)^2=4
but
(-8)^(2/3) = 4(-1)^(2/3) = 4((2/3)(cos (π) + i*sin(π)) and so forth, giving a complex number.
No, it doesn't. sin(π)= 0. The other two cube roots are non-real, of course.
I understand why the latter one works. Why don't the first two?
Thanks.
The first two do also, you just have restricted yourself to real numbers. 64 has three complex cube roots, 4 is one, the other two are non-real. 8 has 3 cube roots, one is 2 and the other two are non-real.
 
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  • #6
They are valid. They give you one of possible three answers, the real one.
 
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  • #7
Thanks, all of those who answered, everything clear now, and I apologize for the typos.
 

Related to ((-8)^2)^(1/3) <> (-8)^(2/3) <> (-8)^(1/3))^2

What does the expression "((-8)^2)^(1/3) <> (-8)^(2/3) <> (-8)^(1/3))^2" mean?

The expression means that we have three different expressions inside parentheses that are raised to different powers and then all of that is squared.

What is the value of "((-8)^2)^(1/3) <> (-8)^(2/3) <> (-8)^(1/3))^2"?

The value of the expression is undefined because it leads to a contradiction. The first part, "((-8)^2)^(1/3)", simplifies to 64^(1/3) which is 4. The second part, "(-8)^(2/3)", simplifies to (-64)^(1/3) which is -4. And the third part, "(-8)^(1/3)", simplifies to (-8)^(1/3) which is -2. Therefore, we have 4 <> -4 <> -2 which is a contradiction.

Why is the expression "((-8)^2)^(1/3) <> (-8)^(2/3) <> (-8)^(1/3))^2" undefined?

The expression is undefined because it leads to a contradiction. The first part, "((-8)^2)^(1/3)", simplifies to 4. The second part, "(-8)^(2/3)", simplifies to -4. And the third part, "(-8)^(1/3)", simplifies to -2. Therefore, we have 4 <> -4 <> -2 which is a contradiction.

Can the expression "((-8)^2)^(1/3) <> (-8)^(2/3) <> (-8)^(1/3))^2" be simplified?

No, the expression cannot be simplified further because it leads to a contradiction. Each part of the expression has a different value, making it impossible to simplify the expression.

What is the importance of understanding the expression "((-8)^2)^(1/3) <> (-8)^(2/3) <> (-8)^(1/3))^2" in mathematics?

Understanding this expression is important because it helps us recognize and avoid contradictions in mathematical operations. It also highlights the importance of following the correct order of operations when simplifying expressions.

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