For positive x and y satisfying x^2 + y^2 = 25, what is the maximum value of xy?
Correct answer: C. 25/2
- A. 5/2
- B. 5
- C. 25/2
- D. 25
Explanation
Since (x - y)^2 is nonnegative, x^2 + y^2 is at least 2xy. Therefore, 25 is at least 2xy, with equality when x = y, so the maximum is 25/2.
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