the area of a circle is A = πr², where r = radius of the circle.
how to find points in the circle? depends on what the scenario is, if you know circle's center and its radius, simply use the distance formula to get any of the points, if you have only the equation of it in standard form, you can use the x,y coordinates with substitution, if you have an sketch, you can get them off the grid, so depends on what you have as components.
