Data Sufficiency

x^3+y^3=?

1) x+y=0
2) x^2-y^2=0


* A solution will be posted in two days.

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

x^3+y^3=?

1) x+y=0
2) x^2-y^2=0


-> In the original condition, there are 2 variables(x,y), which should match with the number of equations.
For 1) 1 equation, for 2) 1 equation, which is likely to make C the answer.
When 1) & 2), you can only substitute 1)x=-y.
Then, x3^+y^3=(-y)^3+y^3=-y^3+y^3=0 is derived, which is unique and sufficient.
Hence, the answer is A.