The problem is that you are attempting to square the cos function. This, for obvious reasons, won't work.
Try this instead: y = sqrt((2*x - 3)/(x+1)) - (cosd((%pi/3)*x))^2
I did several OpenStax and BioMath projects at the Arizona lab last month. We started with Pythagorean adentities. So I could share the the examples. My trigonometry assignment typer custom writing company tasks.