Our angle teta is:
teta = 3pi/4
since that is larger than pi/2 but less than pi that means that our angle lies in II quadrant (x negative y positive)
sin(3pi/4) = √2/2
cosine and tangent of that angle must be negative because of position of the angle.
cos(3pi/4) = -√2/2
tan(3pi/4) = -1