- #1
alvin51015
- 11
- 0
I was wondering if scientists or mathematicians have any use for complex numbers involving negative roots of I as in i=(-1)^(1/2). but my question is more what would be (-1)^(-1/2)?
Also ##\pm i##, as ##\frac{1}{i}=-i## which you can see if you multiply both sides by i.alvin51015 said:but my question is more what would be (-1)^(-1/2)?
HOI said:By the way, there are problems involved with defining "[itex]i= \sqrt{-1}[/itex]'. It can be shown that, in the complex numbers, all numbers have two square roots- so that notation is ambiguous. A better way to define the complex numbers is as pairs of real numbers, (a, b) with addition defined by (a, b)+ (c, d)= (a+ c, b+ d) and multiplication defined by (ab- cd, ad+ bc).
It can be show that this is a field with additive identity (0, 0) and multiplicative identity (1, 0). Further, the field of real numbers can be identified with the subfield (a, 0).
If we then represent multiplication of a real number, a, by a complex number, (b, c) with (a, 0)(b, c) as (ab,, ac), every complex number can be written in the form (a, b)= (a, 0)+ (0, b)= a(1, 0)+ b(0, 1). We have already agreed to represent the real number "1" by "(1, 0)". If we now agree to write [itex]i= (0, 1)[/itex] we have (a, b)= a+ bi.
Better to start with [itex] i^2=-1[/itex].thelema418 said:I don't understand what you mean when you say this notation is ambiguous. The radical sign means principal square root.
sorry, I don't understand the point you are making about ambiguity.symbolipoint said:Better to start with [itex] i^2=-1[/itex].
Exponentiate both sides to the [itex] \frac{1}{2}[/itex] power.thelema418 said:sorry, I don't understand the point you are making about ambiguity.
symbolipoint said:Exponentiate both sides to the [itex] \frac{1}{2}[/itex] power.
Plus or Minus Square Root of negative 1; no more ambiguity.
Then why you say it was ambiguous? You made the correct "implication".thelema418 said:Could you write in greater detail: that is equally confusing. HOI said the notation is ambiguous, and I do not understand if you are also saying the notation is ambiguous. It seems to me you are implying that ##i = \pm \sqrt{-1}##. Further, I do not understand why you would not use ##x^2 = -1##, and then label the principal root ##i## such that ##x_1 = i## and ##x_2 = -i##. There does not appear to be anything ambiguous about this process to me.
symbolipoint said:Then why you say it was ambiguous? You made the correct "implication".
I do not understand you. You also decided that i=sqrt(-1) was ambiguous, and then you found the correct meaning from i^2. The meaning of i is either ambiguous or it is not.thelema418 said:HOI said it was ambiguous. I am asking for clarification about what makes it ambiguous to HOI or anyone who agrees that it is ambiguous.
I do not agree that ##i = \pm \sqrt{-1}##.
When taking the square root of a positive real number, the radical sign means the principle square root -- the square root that is positive.thelema418 said:I don't understand what you mean when you say this notation is ambiguous. The radical sign means principal square root.
Excellent point, but a little extra work to not be confusing. What you mean is that we have this:jbriggs444 said:When taking the square root of a positive real number, the radical sign means the principle square root -- the square root that is positive.
When taking the square root of a negative real number or of a complex number with a non-zero imaginary part there are two square roots. But neither is a positive real number. There is no way to write down a formula for ##i## using real number arguments that could not equally well be considered to yield ##-i##. The labels ##i## and ##-i## are arbitrary in this sense and could be swapped without changing any mathematics.
I think that this is what HOI was trying to get at.
HallsofIvy said:thelema418 wrote "I don't understand what you mean when you say this notation is ambiguous. The radical sign means principal square root. How do you define "principal square root" for complex numbers?".
Before you could use polar coordinates, you would have to define which square root of -1 you are going to place above the real axis and which below. How do you know which one gets the label ##i## and which one gets the label ##-i##?thelema418 said:Personally, I would use polar coordinates and cis notation. I see it like a piece of paper that has a tear down the non-postive real-axis (arbitrarily). As you move counterclockwise from the non-positive real axis, you eventually loop over to the backside of the paper. Continuing to rotate, you are eventually back where you began. The principal root is what occurs on the front page before you get back to where you started; it is contingent on the aforementioned choices.
jbriggs444 said:Before you could use polar coordinates, you would have to define which square root of -1 you are going to place above the real axis and which below. How do you know which one gets the label ##i## and which one gets the label ##-i##?
But -1 and 1 are distinguishable. -1 times -1 is equal to 1. 1 times 1 is not equal to -1. That is not the case for i and -i. The copy of the complex numbers that you get by interchanging the two is isomorphic to the original.thelema418 said:There is no indicators of where to put 1 and -1 on the real y-axis either.
Yes there are. -1 < 0 < 1 whereas there is no ordering of imaginary numbers.thelema418 said:There is no indicators of where to put 1 and -1 on the real y-axis either.
Is this because you are clinging to the definition of ## \sqrt x ## as being the positive square root? There is no such thing as a positive imaginary number.thelema418 said:Notationally, ##i \equiv \sqrt{-1}## seems less ambiguous to me than the proposed ##i^2 = -1##.
That's the whole point - the y-axis (of the Argand plane) does not increase in any direction. Yet again, there is no ordering of imaginary numbers.thelema418 said:And even saying ##(0, 1) = i## does not define whether the y-axis is increasing or decreasing in the downward direction.
The direction of the axis is irrelevant.thelema418 said:And even saying ##(0, 1) = i## does not define whether the y-axis is increasing or decreasing in the downward direction
You are describing a two fold covering of the complex numbers, not the complex numbers themselves.That is not what you want to do when you are defining i itself. You can't define i using a two fold covering of the complex numbers without defining the complex numbers to begin with.I see it like a piece of paper that has a tear down the non-postive real-axis (arbitrarily). As you move counterclockwise from the non-positive real axis, you eventually loop over to the backside of the paper. Continuing to rotate, you are eventually back where you began. The principal root is what occurs on the front page before you get back to where you started; it is contingent on the aforementioned choices.
A geometric description to show the meaning of square root of negative 1 has been derived and a search on YouTube will give some results, at least a few of which will be good. I do not have any specific hyperlink addresses for them.thelema418 said:There is no indicators of where to put 1 and -1 on the real y-axis either. The geometry just seems to be part of an assumptive framework to me, much like rotating counterclockwise and locating the cut. You could really do anything.
This seems like a geometric concern - not a notational ambiguity which is what HOI spoke of. Notationally, ##i \equiv \sqrt{-1}## seems less ambiguous to me than the proposed ##i^2 = -1##. And even saying ##(0, 1) = i## does not define whether the y-axis is increasing or decreasing in the downward direction. HOI claimed this was better than the notational ambiguity with ##i \equiv \sqrt{-1}##.
MrAnchovy said:Yes there are. -1 < 0 < 1 whereas there is no ordering of imaginary numbers.
Is this because you are clinging to the definition of ## \sqrt x ## as being the positive square root? There is no such thing as a positive imaginary number.
pwsnafu said:You are describing a two fold covering of the complex numbers, not the complex numbers themselves.That is not what you want to do when you are defining i itself. You can't define i using a two fold covering of the complex numbers without defining the complex numbers to begin with.
I'm surprised no one has challenged this!MrAnchovy said:there is no ordering of imaginary numbers.
The difference is that, while we can "choose" where we put 1 and -1, either choice makes the real numbers an "ordered field". There is NO choice that makes the complex numbers an ordered field.thelema418 said:There is no indicators of where to put 1 and -1 on the real y-axis either. The geometry just seems to be part of an assumptive framework to me, much like rotating counterclockwise and locating the cut. You could really do anything.
We were being kind! Yes, the complex numbers can be ordered but not in such a way as to give an ordered field.MrAnchovy said:I'm surprised no one has challenged this!
A complex number is a number that contains both a real part and an imaginary part. It is written in the form a + bi, where a is the real part, b is the imaginary part, and i is the square root of -1.
To add or subtract complex numbers, simply combine the real parts and combine the imaginary parts. For example, (3 + 4i) + (2 + 5i) = (3+2) + (4+5)i = 5 + 9i. Similarly, (3 + 4i) - (2 + 5i) = (3-2) + (4-5)i = 1 - i.
The roots of a complex number refer to the solutions of the equation x^2 = a + bi, where a and b are real numbers. This equation can have two solutions, known as the square roots, and can also have multiple solutions depending on the values of a and b.
To simplify negative roots of complex numbers, first rewrite the complex number in polar form. Then, use the property that the square root of a complex number in polar form is equal to the square root of the modulus (or absolute value) times the square root of the argument (or angle divided by 2). Finally, evaluate the square root of the modulus and simplify the square root of the argument if possible.
Geometrically, a complex number can be represented as a point on a two-dimensional plane, known as the complex plane. The real part of the complex number corresponds to the x-coordinate, and the imaginary part corresponds to the y-coordinate. This allows for visualizing operations such as addition, subtraction, and multiplication of complex numbers.