in the unit circle, cos(7pi/4) is in the 4th quadrant which means that the value of cosine is positive,
convert 7pi/4 to degrees using the conversion factor : 180 degrees = pi
you'll get a value of 315 degrees
cos(315) degrees is coterminal with -45 degrees,
therefore the answer is [tex] \frac{ \sqrt{2} }{2} [/tex]
