1.5(degrees) is the scale on my x-axis(relative to the GUI co-ordinates). and 1/80 i.e, 0.0125 is the scale on y-axis(relative to the GUI co-ordinates). The code for first part (positive angles) is working correctly. But all I get is a straight line for the second part(negative angles). Can you please point out where am I getting wrong in my code for second part.
Thank you.

Just adding phases solved my problem, it has been a long time since I used trigonometry or the"ALL SILVER TEA CUPS" idiom. For sine wave I have added a phase of PI/2 and for cosine wave I have added a phase of (1.5)*PI.