Plot the point (5,-5)



Draw the radius vector from the origin to
the point (5,-5):



Indicate with a curved line the angle q measured 
counter-clockwise from the right side of the 
x-axis around to the radius vector.



Draw the x and the y coordinates, forming
a right triangle:



Draw another arc (the red one below) to
represent the REFERENCE angle, the one
with vertex at the origin which is
inside the triangle:



Since 



The side OPPOSITE the reference angle (red arc) is 
y=-5 and the ADJACENT side to the reference
angle is x=5, then the tangent of the angle in
standard position which is q,
(black arc), has the tangent , so we 
end up with

tanq = 

Edwin