Solve an equation with complex numbers

2slowtogofast

1. The problem statement, all variables and given/known data
I am doing a problem where I have to design a controller for a system. I have to solve the below equation for ω

3.1 (ω)^2 - 6.2iω - 20

2. Relevant equations



3. The attempt at a solution

I am not sure how to start It looks like a quadratic but I don't know what to do with the i
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution

Mike706

Looks like a quadratic, quacks like a quadratic. It is probably quadratic. You can use all the normal methods to solve it. The i is just part of the coefficient of the linear term.

micromass

I can't really see an equation anywhere. All I see is an expression in [itex]\omega[/itex]. An equation must contain an "=".

HallsofIvy

Yes, that's a quadratic. What it isn't is an equation! What is the problem really? Do you know the quadratic formula?

Mike706

Sorry, I thought he meant to factor it. Good point!

jackmell

Ok, it's the "i" that's causing the problem for him. That's intimidating to a lot of students not familiar with complex variables.

The think to do 2slow is not be intimidated by them. Treat them just like constants but remember the complex arithmetic i times i is minus one. So you have:

[tex]w^2-6.2iw-20=0[/tex]

(I heard a quack)

alright, that 6.2i is just a constant. Treat it just like if you were solving:

[tex]w^2-aw-20=0[/tex]

as long as you remember to do the complex arithmetic with i's so:

[tex]w=\frac{6.2i\pm\sqrt{(6.2i)^2+80}}{2}[/tex]

Not gonna' have problems with that (6.2i)^2 thing right?