 = 0)
rearranges to give

.
Since we know that

, it follows that

.
The original form of this questions asks the values for there to be two
distinct positions for
M.
The equation given is always satisfied by

.
So, for a given

, there are two positions for M, the one where

and the one where
...except when these are both the same, which occurs when

. Thus, there are two possible positions for
M when
\cup\left(\frac{\pi}{2},\ \frac{2\pi}{3}\right])