abmyers wrote:
In the rectangular coordinate system, are the points (a, b) and (c, d) equidistant from the origin?
(1) a/b = c/d
(2) \(\sqrt{a^2}+\sqrt{b^2} = \sqrt{c^2} + \sqrt{d^2}\)
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 one ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.
You can take values to solve this question quickly:
Statement 1: a/b = c/d
(a,b) and (c,d) may be equidistant from the origin e.g. (1, 1) and (-1, -1) or they may not be e.g. (1, 1) and (2, 2). Not sufficient.
Statement 2: \(\sqrt{a^2}+\sqrt{b^2} = \sqrt{c^2} + \sqrt{d^2}\)
That is, |a|+|b|=|c|+|d|
(a,b) and (c,d) may be equidistant from the origin e.g. (1, 3) and (-1, -3) or they may not be e.g. (1, 3) and (2, 2)
Using both together, |a|+|b|=|c|+|d| and a/b = c/d.
This means that if a/c = 1/2, c/d cannot be 2/4 or -3/-6 etc. c/d has to be either 1/2 or (-1)/(-2). Similarly, if a/b = (-1)/2, c/d = (-1)/2 or 1/(-2))
Any pair of such points will be equidistant. Answer (C).