Step-by-step explanation:
the reference angle is the smallest angle difference between the defining terminal arm of the angle and the x-axis. it is always positive.
if an angle is smaller than 90°, then it is is own reference angle.
7pi/4 is 1pi/4 (or simply pi/4) short of a full circle (2pi or 8pi/4).
therefore, if is easy to see that this pi/4 is the reference angle (45°).
tan(7pi/4) = -1, while tan(pi/4) = 1.
for every 45° angel in every quadrant the absolute values of sine and cosine are equal.
but in quadrant 1 both, sine and cosine, are positive, while in quadrant 4 sine is negative and cosine is positive.
and since tan = sine/cosine, this gives us the results above.