Coordinate geometry-DS

**dimwit** · 12-23-2008, 10:32 PM

In rectangular coordinate system does the line k intersect quadrant II?
1. The slope of k is -1/6
2. The y intercept of k is -6

**gmat_t1** · 12-24-2008, 01:29 AM

Neither of these are sufficient. Answer should be (E)

**sjd00d** · 12-24-2008, 01:33 AM

D.

1. slope of k = -1/6, line intersecting 2nd quad. would have a positive slope (try this with a pair of numbers (0,1) & (-6,0)). Means line doesn't intersect 2nd quad. Suff.

2. this is the easy one, no line can pass through the y intercept -6 and yet intersect 2nd quad. Suff.

**dimwit** · 12-24-2008, 02:23 AM

The Official Answer is A

**tytyros** · 12-24-2008, 06:00 PM

-ve slope passes through QII AND QIV....so 1 is sufficient
as regards condtn 2, line may or may not pass through QII
Official Answer is A

**sjd00d** · 12-24-2008, 07:25 PM

i am confused here then. intersecting a quadrant means a line that intersects both the x and y axis of that quadrant, is that not correct? If that is then how can a line intersect quad II if one of its point is -6. What am I missing?

**tytyros** · 12-24-2008, 07:36 PM

intersecting quadrant ....literally means does the line lies in that quadrant...this is a yes/no question. y intercept is the term c in mx+c equation....if c=-6 then imagine a line across Quandrant III, IV, and I....and also imagine a line across Quadrant IV, III and II.
and now reconsider answering yes/no question from the given conditions....answer is A is sufficient

**sjd00d** · 12-25-2008, 08:00 PM

so, essentially you are saying that intersecting a quad means "does the line pass through that quad.", right? Coz based on your explanation i am still not convinced if that's what you mean. I thought intersecting 2nd quad means does the line pass through positive y (where x = 0) and negative x (where y =0), given that y = -6 when x = 0 in stmt. II, how is that possible.

Sorry to be dragging this a bit but a clearer explanation would help.

**WordNeard** · 12-26-2008, 06:28 AM

Official Answer is A
any negative sloping line will go through the 2nd and 4th quadrant. any positive sloping line will go through the 1st and 3rd quadrant. note however that it is possible for a positive sloping line to intersect the 2nd or 4th, but not both, and it is possible for a negative sloping line to intersect the 1st and 3rd, but not both.

my advice: if you want to visualise this, draw the following lines:
1. y = 1*x + 6 [intersects 1st and 2nd and 3rd].
2. y = 1*x + 0 [intersects 1st and 3rd].
3. y = 1*x - 6 [intersects 1st, 3rd and 4th]
4. y = -1*x + 6 [intersects 1st, 2nd, and 4th]
5. y = -1*x + 0 [intersects 2nd, and 4th]
6. y = -1*x - 6 [intersects 2nd, 3nd, and 4th].

**sjd00d** · 12-26-2008, 06:32 PM

ok, i give up. will try to do some research as i am obviously wrong and not understanding something basic..if you go by the definition of intersecting a quadrant as ...

"I thought intersecting 2nd quad means that the line pass through positive y (where x = 0) and negative x (where y =0)"

then in case of stmt. 1) I would say sufficient coz it WILL NOT (you guys are saying it will)

Stmt 2) if the line goes through a point 0,-6 then i am saying that no way in hell will it intersect quad II per my definition of intersection (which is WRONG)

Thx guys for being patient. No need to post any more..i'll just have to do some digging.