Deriving power attenuation in TE10 rectangular waveguide

[Anabelle37]

Homework Statement

Show from general considerations that the attenuation of power in the rectangular waveguide (TE10 mode propagating in z-direction) is:
P(z)=P(0)exp(-2k''z)
where k'' is the imaginary part of the wavevector in the phasor exp(j(wt-kz))

Homework Equations

power is proportional to the square of the amplitude

The Attempt at a Solution

tried squaring the phasor and setting k=k'+k''j but did not get right answer.
Please help!

 

[olivermsun]

What happens when j and j meet in the exponential?

 

[Anabelle37]

think there is a typo in the question it should be P(z)=P(0)exp(2k''z).

after squaring the phasor I get: P(z) = exp(2j(wt-k'z))exp(2k''z)

then i don't know what to do to get in right form.