It is probably easy as hell but I just drew a blank and my algebra isn't too hot though I've tried to rely less on my calculator. Haha funny story about that: in one of my first EE classes, intro to signal processing, this guy who sat next to me was a senior EE but re-taking it. He had said one day "this is what makes me an engineer maaan", as he raises his 89 in the air with a big smile. Anyway...

I needed to solve for two variables, which I will call x and y to make it easy.

eqn1:

182e-6 = .5 * x * (3 - y)^2

eqn2:

235e-6 = .5 * x * (4 - y)^2

eqn3:

433e-6 = .5 * x * (5 - y)^2

I guess I would only need 2 equations if there are only 2 unknowns. My ideas:

1) divide one equation by the other, but IIRC there is something like I can't just cancel out the square cause I'd lose the sign. I then end up with two values, and eliminate the value that doesn't make sense, leaving me with the value for x (or y) which I would then substitute into any equation to solve for y (or x).

2) just re-arrange any equation and solve for x (or y) in terms of the other variable, plug that into another equation and solve for y (or x), then with that value I could get x (or y) as a number.

Would either of these work? I'm not sure if where I said "any equation" is correct. Or is there just a common, better way of doing something like this?

**my elegant solution (not important to my question)**

Since I was pressed for time doing the rest of the problem, and unsure how to solve those equations, I did a good ol' guess and check.

It was solving for values for a MOSFET given a bunch of other ones, and since I knew a common threshold voltage for a n-MOSFET was 1.0 V, I started with it and by my third guess, the resulting i_D was near exact one of the givens. w00t!

So I think I got them right but maybe not, or I got lucky, and I should know how to do this anyway.