In degrees: 3π/4 radians = 135°
Angle of x=135° is in the 2nd Quadrant and has negative cos x values and positive sin x values.
cos 135° = cos ( 90° + 45°)= - sin 45° =\(- \frac{ \sqrt{2} }{2}\)
sin 135° = sin ( 90° + 45° ) = cos 45° =\(\frac{ \sqrt{2} }{2}\). You can also see the graph in the attachment.
