Question 23293
Draw the picture.
The point is "m" to the left of the y-axis.
Now cosQ =m =m/1.  The point is "1" away 
from the origin because it is on a unit-
circle.  Using Pythagoras  you get 
1^2 = m^2 + ?^2.
The ? = sqrt(1-m^2) but it is negative because
it is a Y-value in the III quadrant.
P is the point (m,-sqrt(1+m^2).

Cheers,
Stan H.