### Roots and Coefficients

If xyz = 1 and x+y+z =1/x + 1/y + 1/z show that at least one of these numbers must be 1. Now for the complexity! When are the other numbers real and when are they complex?

### Target Six

Show that x = 1 is a solution of the equation x^(3/2) - 8x^(-3/2) = 7 and find all other solutions.

### 8 Methods for Three by One

This problem in geometry has been solved in no less than EIGHT ways by a pair of students. How would you solve it? How many of their solutions can you follow? How are they the same or different? Which do you like best?

# Impedance Can Be Complex!

##### Age 16 to 18Challenge Level

Part 1:

$P = IV$

I = $\frac{E}{Z_1 + Z_2} = \frac{E}{Z_1cos\theta + Z_2cos\phi + i(Z_1sin\theta + Z_2sin\phi)}$

|I| = $\frac{E}{\sqrt{(Z_1cos\theta + Z_2cos\phi)^2 + (Z_1sin\theta + Z_2sin\phi)^2}}$

The real power transferred to $Z_2$: P = I^2 R

P = $I^2 Z_2cos \phi = \frac{E^2 Z_2cos \phi}{Z_1^2 + Z_2^2 + 2Z_1Z_2(cos \theta cos \phi + sin \theta \phi)}$= $\frac{E^2 Z_2cos \phi}{Z_1^2 + Z_2^2 + 2Z_1Z_2cos( \theta - \phi )}$

Part 2:

To find the maximum power; we can differentiate the power expression with respect to $Z_2$ and set the derivative equal to zero.

$\frac{dP}{dZ_2} = \frac{d}{dZ_2}\frac{E^2 Z_2cos \phi}{Z_1^2 + Z_2^2 + 2Z_1Z_2cos( \theta - \phi )}$

Let U = $E^2 Z_2cos \phi$

Let V = $Z_1^2 + Z_2^2 + 2Z_1Z_2cos( \theta - \phi )$

$\frac{dP}{dZ_2} = \frac{VU' - UV'}{V^2}$

V' = $2Z_2 + 2Z_1 cos ( \theta - \phi)$

U' = $E^2 cos \phi$

Substituting thses values into the expression and setting it equal to zero we find that:

$Z_1 = Z_2$

For maximum power transfer between load and source we must therefore match the internal impedance of the load with the impedance of the source