Problem Solving

In the xy-plane, the points (c, d), (c, -d), and (-c, -d) are three vertices of a certain square. If c < 0 and d > 0, which of the following points is in the same quadrant as the fourth vertex of the square?

A. (-5, -3)
B. (-5, 3)
C. (5, -3)
D. (3, -5)
E. (3, 5)

IMPORTANT: c < 0 and d > 0
In other words, c is NEGATIVE and d is POSITIVE

Let's examine each of the three given vertices:

(c, d): So, we get (NEGATIVE, POSITIVE). This vertex is in quadrant II
(c, -d): So, we get (NEGATIVE, -POSITIVE), which simplifies to (NEGATIVE, NEGATIVE). This vertex is in quadrant III
(-c, -d): So, we get (-NEGATIVE, -POSITIVE), which simplifies to (POSITIVE, NEGATIVE). This vertex is in quadrant IV

So, the last vertex must be in quadrant I
Only (3, 5) is in quadrant I

Answer: E

Cheers,
Brent

Hi dqure040,

You might find it helpful to TEST VALUES.

We're told that C < 0 and D > 0.

Let's TEST
C = -2
D = +2

We're given 3 of 4 co-ordinates for a square....
(C,D) = (-2, +2) which is in the 2nd Quadrant
(C, -D) = (-2, -2) which is in the 3rd Quadrant
(-C, -D) = (+2, -2) which is in the 4th Quadrant

Since we're dealing with a square, the 4th co-ordinate will be in 1st Quadrant...There's only one answer that's also in the 1st Quadrant...

Final Answer: E

GMAT assassins aren't born, they're made,
Rich