How to calculate CD distance?

Question

Mathematics

Help plz))
Something is stupid...
AB= r;(known value)
BE= r;(known value)
BC = x;(known value)
Need to get a CD

Answer 1

DC = r - sqrt(BC * (2 * r - BC))

Answer 2

(1-cos(arctan(CE/r)))*r
Through the arctangent we find the angle, through the cosine we find the projection of D onto the X axis, and when we subtract the cosine from unity, we get just the distance DC for the unit circle, multiplying by the radius, we get the physical distance DC. It is important not to confuse angle measures. If the arc tangent is in radians, then the cosine is also needed, which of the radians is considered or convert radians to degrees and calculate the cosine of the angle in degrees