the square root of 4 + the square root of 16 = 6 which is a rational number.
the given expression is
we split the middle term to obtain;
we factor to get;
we factor further to obtain;
we factor the negative 1 to get;
so, is a semi-circle, half a circle, recall a circle has a total of 360°, so half of that will be 180°.
the diameter of that circle is 10, so its radius is half that, or 5.