# Complex number question

1. Jan 27, 2010

### lockedup

1. The problem statement, all variables and given/known data If $$z = \frac{a}{b}$$ and $$\frac{1}{a + b} = \frac{1}{a} + \frac{1}{b}$$, find z.

2. Relevant equationsI'm pretty sure z is a complex number.

3. The attempt at a solutionI have no idea where to start. The teacher did nothing like this in class. I tried something that involved combining the fractions on the right hand side and then cross-multiplying with the fraction on the left hand side. I played around with that for a few minutes but it didn't give me anything.

2. Jan 27, 2010

### PhysicsMark

I am confused about what you are asking. z is defined. Are you trying to get z in different terms than above? Or perhaps in cartesian/standard or polar form?

3. Jan 27, 2010

### l'Hôpital

Keep playing. It works out.

4. Jan 27, 2010

### Dick

Multiply both sides of your equation by (a+b) and try to reduce the right side to terms that are constants or a/b, or b/a. a/b=z. Doesn't that make b/a=1/z? Write it all in terms of z. Think 'quadratic equation'.

5. Jan 27, 2010

### lockedup

I think I got it. I substituted zb for a. I combined and cross multiplied again. I ended up with $$z = \frac{-1}{2} \pm \frac{i\sqrt{3}}{2}$$

Now I need to check it...

6. Jan 27, 2010

### lockedup

It checks! w00t \O/