Answers

2015-07-20T19:06:23+08:00
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  \frac{ \sqrt{2} }{2}

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