How to make a curved triangle with exact measurments firstly, i would like to apologise for the title, it may not be on point. 

secondly, i would like to thank all of you who always help and answer noob questions. I have learned a lot form you guys. 

here is my question: 

i am trying to make a small triangle box, to 3d print. And that box needs to have a sliding door. 
the first problem i am facing is getting an homogenous rounded edge on the hypotenuse, which makes it difficult to model the sliding door. 





what am i doing wrong?
I think the easiest way to get the results you want is to start with a cylinder. Simply add a cylinder, choose triangle fan as the cap fill type, and from top view delete the mesh you don't need (3/4 of it). Then fill the 2 flat sides (one face each) and you're done.