inequalities with imaginary numbers
PostPosted: Thu Sep 01, 2005 10:37 pm
by Slater
... yeah, how?
Like x^2 - 2x + 2 > 0
Which should factor to (x - 1 - i)(x - 1 + i) > 0
This isn't crittically important since my homework grade doesn't affect my overall grade, but the point of homework in college like that is to learn... any teachers?
PostPosted: Sun Sep 04, 2005 3:41 pm
by Technomancer
It depends on exactly what they're asking here. I suspect that they're only interested in the set of real numbers x such that the inequality holds in which case, the complex solutions are quite immaterial. On the other hand if they're interested in all values of x that satisfy the inequality, you have to define what the inequality means for complex numbers, which is something that is not immediately clear.
Given that they're not specifically stating that the magnitude of the LHS be greater than zero (which would be trivial), I think we can safely decide that the solutions must be all real and that the imaginary component vanishes. In this case, you need to set x=a+b*i, and expand your equation by substituting in your new definition of x. This will give you two equations that you must solve. One will be all real and must be greater than zero, and the second will be all imaginary and must be equal to zero.