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This problem trains for: SAT-I, AMC-8, GMAT, AMC-10.

If x and y are rational numbers satisfying: what is the value of x+y?

Square both sides and simplify:  Since x and y are rational numbers the irrational quantity on the left side must equal the irrational quantity on the right side and similarly for the rational quantities. This results in two equations: one for the rational parts and one for the irrational parts. m4  Solve the system of two equations:  by solving for y in the first equation and substituting in the second equation:  and obtain a bi-quadratic equation: We can solve this equation similarly to a quadratic equation but not forgetting that it will usually have four roots.  Since x has been specified as rational, only the rational solutions qualify.

Since x and y are either both positive or both negative, the possible sums for x and y are in the set: 