Is the Complex Conjugate of Sin Equal to Sin of the Conjugate?

In summary, the equation (\sin{z})^* = \sin{z^*} does not hold true for complex numbers. Instead, the correct equation is (\sin{z})^* = \frac{1}{2i} (e^{iz} - e^{-iz}). This is due to the presence of the imaginary unit "i" in the denominator, which accounts for the difference in signs when taking the complex conjugate.
  • #1
Pythagorean
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Homework Statement



does [tex](\sin{z})^* = \sin{z^*}[/tex]?

(where z is a complex number)

Homework Equations



[tex]\sin{z} = \frac{1}{2} (e^{iz} - e^{-iz})[/tex]

The Attempt at a Solution



[tex](\sin{z})^* = \frac{1}{2} (e^{iz} - e^{-iz})^*
= \frac{1}{2} (e^{-iz^*} - e^{iz^*})
= -\frac{1}{2} (e^{iz^*} - e^{-iz^*})
= -sin(z^*)[/tex]

...but my teacher told us ahead of time that they should be equivalent. I'm not seeing my mistake. Thank you for your time and energy.

I will also note that the same problem for cos only worked out to be equivalent because of the commutative rule. This doesn't work for sin, since it's exponential terms differ in their signs.
 
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  • #2
Here's your error:
[tex]\sin{z} = \frac{1}{2} (e^{iz} - e^{-iz})[/tex]
is wrong.

[tex]\sin{z} = \frac{1}{2i} (e^{iz} - e^{-iz})[/tex]


It's the "i" in the denominator that will take care of that sign.
 
  • #3
ah, right, old habit from the days of real.

Thank you HallsofIvy
 

1. What is the complex conjugate of sin?

The complex conjugate of sin is the trigonometric function that represents the ratio of the opposite side to the hypotenuse in a right triangle. It is often written as sin(x) or simply sin.

2. How is the complex conjugate of sin calculated?

The complex conjugate of sin is calculated by taking the sine of an angle and then changing the sign of the imaginary component. For example, if sin(x) = a + bi, then the complex conjugate of sin(x) is a - bi.

3. What is the relationship between the complex conjugate of sin and the sine function?

The complex conjugate of sin is the complex number that is obtained by changing the sign of the imaginary component of the sine function. This means that the two functions are closely related, but they are not the same.

4. What are the properties of the complex conjugate of sin?

The properties of the complex conjugate of sin include being a complex number, having a real component that is equal to the sine of an angle, and having an imaginary component that is equal to the negative of the sine of an angle.

5. How is the complex conjugate of sin used in mathematics and physics?

The complex conjugate of sin is used in mathematics and physics to simplify equations and solve complex problems involving trigonometric functions. It is also used to find the magnitude and phase of a complex number, which is important in many scientific applications.

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