How to draw 50 degree , 80 degree and 40 degree ?

We can draw 40 degree, 50 degree and 80 degree using protractor as shown below:

Construction of 40 degree:

Here $\angle \mathrm{AOB} = 40°$

Construction of 50 degree:

Here $\angle \mathrm{AOB} = 50°$

Construction of 80 degree:

Here $\angle \mathrm{AOB} = 80°$