Displacement of Underdamped Oscillation: Maximum and Minimum Occurrence?

[end3r7]

Homework Statement

Show that the local maximum or minimum for the displacement of an underdamped oscillation does not occur halfway between the times at which the mass passes its equilibrium point.

Homework Equations

x = e^{-\frac{ct}{2m}}(A cos(wt) + B sin(wt))
x = K e^{-\frac{ct}{2m}} sin(wt + P)

T = \frac{2\pi}{w}

w = angular frequency = \frac{\sqrt{4mk - c^2}}{2m}
Because the system is underdamped, 4mk > c^2

T = period

The Attempt at a Solution

I said sin(wt + P) attains its maximum when wt + P = (4k + 1)\frac{\pi}{2} and min when wt + P = (2k + 1)\frac{\pi}{2}
Likewise, it crosses the equilibrium when wt + P = k\pi.

Thus the period for a pass by equilibrium is simply \frac{pi}{w}

So I did k\pi + \frac{\pi}{2w} = (2k + \frac{1}{w})\frac{\pi}{2}
But this does cross a min if w = 1... where did I go wrong?

 

[end3r7]

I also have a follow up question. Given a general equation, how do I estimate the parameters c, m, k

 

[end3r7]

Sorry for bumping this, but I'm actually not even sure if I understand the question fully. If anyone could at least tell me whether I'm correctly interpreting the question...