Carcass wrote:
If \(y-x > x + y\), where x and y are integers, which of the following must be true?
I. \(x < 0\)
II. \(y > 0 \)
III. \(xy > 0 \)
A. I only
B. II only
C. I and II only
D. I and III only
E. II and III only.
Take:
y - x > x + yAdd x to both sides:
y > 2x + ySubtract y from both sides:
0 > 2xDivide both sides by 2 to get:
0 > xSo, statement I must be true, but statements II and III are not necessarily true.
Answer: A
Aside: We can show that statement II is not necessarily true with the following counterexample...
If
y - x > x + y, it could be the case that x = -1 and y = -2
In this case, y < 0, which means statement II is not necessarily true
Aside: We can show that statement III is not necessarily true with the following counterexample...
If
y - x > x + y, it could be the case that x = -1 and y = 1
In this case, xy < 0, which means statement III is not necessarily true