If x and y are positive, what is the value of x – y?
(1) (x2 – y2) / (x + y) = 4
(2) x + y = 7
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.
My Answer is C, but OA is A.<X平方-Y平方>/X+Y=4
可化为 <X+Y><X-Y>/X+Y=4
分式同时约<X+Y>,得<X-Y>=4
所以A 为正确答案
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