In a nutshell, the overlap between what my complex analysis professor teaches and what he assigns homework over is the null set. Anyway, here's the problems:
1) Solve: sin(z) = (3/4) + i(1/4)
2) Solve: sin(z) = 4
For 1), I've tried writing sin(z) in the form [e^iz - e^-iz]/2i. Then I multiplied through by an e^iz and obtained the following:
e^2iz + [1/2 - (3/2)i]*(e^iz) - 1 = 0
Used the quadratic formula and found the roots of e^iz. However, this leaves me with a really nasty equation, which I have to take the natural log of and divide by i to solve for z. Surely there's an easier way, right?
For 2, I'm tempted to say that there are no solutions for z which solve the equation (since sin(x) can never be greater than 1 for a real number x). However, I'm afraid this may be an oversimplification.
Any help would be appreciated.
1) Solve: sin(z) = (3/4) + i(1/4)
2) Solve: sin(z) = 4
For 1), I've tried writing sin(z) in the form [e^iz - e^-iz]/2i. Then I multiplied through by an e^iz and obtained the following:
e^2iz + [1/2 - (3/2)i]*(e^iz) - 1 = 0
Used the quadratic formula and found the roots of e^iz. However, this leaves me with a really nasty equation, which I have to take the natural log of and divide by i to solve for z. Surely there's an easier way, right?
For 2, I'm tempted to say that there are no solutions for z which solve the equation (since sin(x) can never be greater than 1 for a real number x). However, I'm afraid this may be an oversimplification.
Any help would be appreciated.
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(1) There isn't an easier way to do this than what you did, but it is not as hard as you think.
The equation you have so far, e^(2iz) + [1/2 - (3/2)i]e^(iz) - 1 = 0, is correct. I'm going to multiply both sides of this by 2 to make the formatting easier, and it will probably make the numbers easier to work with as well, giving:
2e^(2iz) + (1 - 3i)e^(iz) - 2 = 0.
Then, by the Quadratic Formula:
e^(iz) = {-(1 - 3i) ± √[(1 - 3i)^2 - 4(2)(-2)]}/[2(2)]
= [-1 + 3i ± √(1 - 6i + 9i^2 + 8)]/4
= [-1 + 3i ± √(1 - 6i - 9 + 8)]/4, since i^2 = -1
= [-1 + 3i ± √(-6i)]/4.
We now need to compute the square root of √(-6i).
The square root (or any root for that matter) of a complex number is another complex number, so suppose that √(-6i) has a square root of a + bi where a and b are real numbers. Then:
a + bi = √(-6i).
Squaring both sides of this gives:
(a + bi)^2 = -6i ==> (a^2 - b^2) + 2abi = -6i.
Comparing real and imaginary parts yields the system:
a^2 - b^2 = 0 and ab = -3.
The equation you have so far, e^(2iz) + [1/2 - (3/2)i]e^(iz) - 1 = 0, is correct. I'm going to multiply both sides of this by 2 to make the formatting easier, and it will probably make the numbers easier to work with as well, giving:
2e^(2iz) + (1 - 3i)e^(iz) - 2 = 0.
Then, by the Quadratic Formula:
e^(iz) = {-(1 - 3i) ± √[(1 - 3i)^2 - 4(2)(-2)]}/[2(2)]
= [-1 + 3i ± √(1 - 6i + 9i^2 + 8)]/4
= [-1 + 3i ± √(1 - 6i - 9 + 8)]/4, since i^2 = -1
= [-1 + 3i ± √(-6i)]/4.
We now need to compute the square root of √(-6i).
The square root (or any root for that matter) of a complex number is another complex number, so suppose that √(-6i) has a square root of a + bi where a and b are real numbers. Then:
a + bi = √(-6i).
Squaring both sides of this gives:
(a + bi)^2 = -6i ==> (a^2 - b^2) + 2abi = -6i.
Comparing real and imaginary parts yields the system:
a^2 - b^2 = 0 and ab = -3.
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