Incorrect values with some trigonometric functions

[jeanjpersia]

I don't have too much time with this my HP prime rev:C and in an exam, I realized that when I try to put things like Cos(π/2) the answer is not the number that I want, I have a similar problem with graphics if I put the cursor in (1,0) the calculator says that I have in (0.99999999,0).

If someone knows what I need to change in settings to solve the problem, it would be great. thanks in advance!

Here an example: https://imgur.com/649PMSj