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Answer:
 RS = RT = 2
Explanation:
The two tangents from a point are the same length.
 RS = RT
 y = y^2/2
 y^2/2 -y = 0
 y(y/2 -1) = 0 . . . . factor out y
Values of y that make these factors zero are ...
 y = 0 . . . . . . . . true if points R, S, T are coincident on the circle
 y/2 -1 = 0 ⇒ y = 2
Then the segment lengths are ...
 RS = RT = 2