Expression 4: StartFraction, "x" left parenthesis, "r" Subscript, 2 , Baseline minus "r" Subscript, 1 , Baseline , right parenthesis plus left parenthesis, "r" squared plus "r" squared , right parenthesis Over 2 StartRoot, "r" Subscript, 1 , Baseline "r" Subscript, 2 , Baseline , EndRoot , EndFraction less than or equal to "y" less than or equal to StartRoot, "R" squared minus "x" squared , EndRootxr2−r1+r21+r222r1r2≤y≤R2−x2