karthikpandian19 wrote:Is x2 - y2 a positive number?
(1) x - y is a positive number.
(2) x + y is a positive number.
x² - y² = (x + y)(x - y) and x² - y² will be positive only if both (x + y) and (x - y) are positive or both (x + y) and (x - y) are negative.
(1) x - y is a positive number.
If x = 5, y = 2, x - y = positive; here x + y = positive
If x = -2, y = -5, x - y = positive, but x + y = negative
No definite answer; NOT sufficient.
(2) x + y is a positive number.
If x = 2, y = 7, x + y = positive; here x - y = negative
If x = 5, y = 2, x + y = positive, here x - y = positive
No definite answer; NOT sufficient.
Combining (1) and (2), we can definitely say that x² - y² will be positive; SUFFICIENT.
The correct answer is
C.
