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Find the real and imaginary part of sin(4+3i)

by tatiana_eggs
Tags: imaginary, real, sin4
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tatiana_eggs
#1
Sep18-10, 05:21 PM
P: 70
1. The problem statement, all variables and given/known data

Find the real and imaginary part of sin(4+3i)

2. Relevant equations

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

cosx = [tex]\frac{e^z + e^(-z)}{2}[/tex]

sin(iy) = i[tex]\frac{e^y - e^(-y)}{2}[/tex]

cos(iy) = [tex]\frac{e^y + e^(-y)}{2}[/tex]

various trig identities

3. The attempt at a solution

So I used sin(x+y) trig identity and got
sin4*cos3i + sin3i*cos4

I turned them all into exponents using the appropriate equations stated in (2).

I got to a point where nothing is really calculable by hand/head. Is there an easier way to do this or does the calculator need to be used at a certain point to calculate the real part(terms grouped w/o i) and the imaginary part (terms grouped with i).

If so, then I guess I need help getting the terms grouped together to calculate the real and imaginary parts.

Where I am stuck is at:

[tex]\frac{e^{3+4i}+e^{-3+4i}-e^{3-4i}+e^{-3-4i}}{4i}[/tex] +
[tex]\frac{e^{3+4i}-e^{-3+4i}+e^{3-4i}-e^{-3-4i}}{4}[/tex]

(the two fractions should be added together)

Now what should I do with all these lovely exponents? Should I have even gone this route?
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HallsofIvy
#2
Sep18-10, 06:13 PM
Math
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P: 39,553
Quote Quote by tatiana_eggs View Post
1. The problem statement, all variables and given/known data

Find the real and imaginary part of sin(4+3i)

2. Relevant equations

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

cosx = [tex]\frac{e^z + e^(-z)}{2}[/tex]

sin(iy) = i[tex]\frac{e^y - e^(-y)}{2}[/tex]

cos(iy) = [tex]\frac{e^y + e^(-y)}{2}[/tex]

various trig identities

3. The attempt at a solution

So I used sin(x+y) trig identity and got
sin4*cos3i + sin3i*cos4

I turned them all into exponents using the appropriate equations stated in (2).

I got to a point where nothing is really calculable by hand/head. Is there an easier way to do this or does the calculator need to be used at a certain point to calculate the real part(terms grouped w/o i) and the imaginary part (terms grouped with i).

If so, then I guess I need help getting the terms grouped together to calculate the real and imaginary parts.

Where I am stuck is at:

[tex]\frac{e^{3+4i}+e^{-3+4i}-e^{3-4i}+e^{-3-4i}}{4i}[/tex] +
[tex]\frac{e^{3+4i}-e^{-3+4i}+e^{3-4i}-e^{-3-4i}}{4}[/tex]

(the two fractions should be added together)

Now what should I do with all these lovely exponents? Should I have even gone this route?
Now use [itex]e^{3+ 4i}= e^3cos(4)+ i e^3sin(4)[/itex], etc.
tatiana_eggs
#3
Sep18-10, 06:46 PM
P: 70
That was just the hint I needed, Halls. Thanks! Finally got it.


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