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Which of the following is the equation of the line in the xy-plane tha [#permalink]

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14 Jun 2016, 11:43

How can I tackle this question? The answer is B but I do not understand why? If the equation of a line is in the form y = mx + b. How could y = 3 have a slope of 0? Moreover, why can't statement I be the answer?

Re: Which of the following is the equation of the line in the xy-plane tha [#permalink]

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12 Jul 2016, 06:56

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saiesta wrote:

How can I tackle this question? The answer is B but I do not understand why? If the equation of a line is in the form y = mx + b. How could y = 3 have a slope of 0? Moreover, why can't statement I be the answer?

Quote:

My two cents: Which of the following is the equation of the line in the xy-plane that has slope 0

(I) x = 2 (II) y = 3 (III) x + y = 0

Consider the equation: y=mx+c ------------ Equation (1)

Now, given is that slope is 0, so, m=0 If you substitute in Equation (1), you get y=3 Now, y=3 is a horizontal line on the xy-plane, which has a slope ZERO. Also, consider x=2, x=2 is a vertical line, and slope of a vertical line is undefined, As the points on a vertical line would have same x-coordinate value. slope = m = (y2-y1)/(x2-x1) Option III, you have y=-x, so slope = -1.

Re: Which of the following is the equation of the line in the xy-plane tha [#permalink]

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12 Jul 2016, 23:54

the equation of a line is given as (the point slope form)

y=mx+c where m is the slope

for a line to have slope as 0 m should be equal to 0

so the above equation can be written as y=c

among the answer choices only B satisfies the criteria.

if we draw line in statement one , we will get a line parallel to y axis. now , slope is also given as tan@ = perpendicular/base ,which in this case is undefined.

Which of the following is the equation of a line in the xy-plane that [#permalink]

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02 Sep 2016, 11:44

Which of the following is the equation of a line in the xy-plane that has slope 0?

I. x=2 II. y=3 III. x+y=0

A) I only B) II only C) III only D) I and II E) II and III

So I'm a little confused. I thought for Statement I and II when the equation of a line is like that it always means the slope is 0.

For Statement I we know that the X coordinate is always 2 so one method is to plug in coordinates for Y and then flind the slope so (2,10) and (2,-3) so we get -3-10/2-2 =-13/0=undefined

Then for statement II same idea. Y is always 3 so we can do (2,3) and (5,3). Slope will equal 0.

Statement III confuses me. I guess I always thought x=3 the slope was 0? Can someone clarify?

Re: Which of the following is the equation of a line in the xy-plane that [#permalink]

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02 Sep 2016, 11:56

The equation of a line is y = mx + c, where m is the slope and c is the y intercept. Slope 0 implies that the line is parallel to the x axis. which means that y intercept should be constant and x intercept 0 i.e the line will never intersect the X axis or is the x axis itself clearly, y = (m=0) (x = 0) + c i.e y = c will be the equation of such a line. In this case y = 3. In general y = n ( where n is -infinity to infinity) is the equation of a line with slope 0. Hope this is clear.

Re: Which of the following is the equation of a line in the xy-plane that [#permalink]

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02 Sep 2016, 12:03

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joannaecohen wrote:

Which of the following is the equation of a line in the xy-plane that has slope 0?

I. x=2 II. y=3 III. x+y=0

A) I only B) II only C) III only D) I and II E) II and III

So I'm a little confused. I thought for Statement I and II when the equation of a line is like that it always means the slope is 0.

For Statement I we know that the X coordinate is always 2 so one method is to plug in coordinates for Y and then flind the slope so (2,10) and (2,-3) so we get -3-10/2-2 =-13/0=undefined

Then for statement II same idea. Y is always 3 so we can do (2,3) and (5,3). Slope will equal 0.

Statement III confuses me. I guess I always thought x=3 the slope was 0? Can someone clarify?

Points related to slope:

1. If a line is vertical, the slope is not defined, line is parallel to Y-axis and crosses quadrant I and IV, if the X intersect is positive and quadrant II and III, if the X intersect is negative. Equation of such line is , where a is x-intercept.

In our case x = 2. undefined slope.

2. If a line is horizontal it has a slope of 0 , is parallel to X-axis and crosses quadrant I and II if the Y intersect is positive OR quadrants III and IV, if the Y intersect is negative. Equation of such line is y=b, where b is y intersect.

In our case y = 3. Slope is 0.

3. The general form of the equation is ax+by+c =0 .

Re: Which of the following is the equation of the line in the xy-plane tha [#permalink]

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14 Sep 2016, 23:53

msk0657: Couldn't quite understand the concept in point no:3. General form of the equation is ax+by+c=0.

If y=-x, then substituting the same is the equation y=mx+b, would give -1=m+b, m=-1-b. But then without knowing value of 'b', 'm' cannot be determined. Can you explain.?

Re: Which of the following is the equation of the line in the xy-plane tha [#permalink]

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15 Sep 2016, 02:38

narendran1990 wrote:

msk0657: Couldn't quite understand the concept in point no:3. General form of the equation is ax+by+c=0.

If y=-x, then substituting the same is the equation y=mx+b, would give -1=m+b, m=-1-b. But then without knowing value of 'b', 'm' cannot be determined. Can you explain.?

Hi Narendran,

1. General form. The general form of the equation of a straight line is ax+by+c = 0. Where a,b and c are arbitrary constants. This form includes all other forms as special cases. For an equation in this form the slope is -a/b and the y intercept is -c/b.

2. Point-intercept form. y = mx+b. Where: m is the slope of the line; b is the y-intercept of the line; x is the independent variable of the function y .

We know the standard equation form is ax+by+c=0 , which you mentioned correctly. We can write like this y = (-a/b)x + (-c/a) , here y intercept is (-c/a) and slope is (-a/b).

We are given only y+x = 0 and let's write this one in the above converted form i.e. => y = (-1)x + 0 , we are not given any b value i.e. y-intercept value and if we compare equation with the standard one then we can see slope is -1 and it is -ve value.

Hope this is clear...Please let me know if this is not clear.

Re: Which of the following is the equation of the line in the xy-plane tha [#permalink]

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26 Sep 2017, 22:09

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saiesta wrote:

Which of the following is the equation of the line in the xy-plane that has slope 0

(I) x = 2 (II) y = 3 (III) x + y = 0

A. I only B. II only C. III only D. I and II only E. II and III only

15 Second approach if you know how to visualize the lines spatially (Ron purewal method)

Basically anything parallel to Y axis has a slope undefined, parallel to X axis has slope 0, 45 Degrees has slope 1 in first quadrant, and 45 Degrees has slope -1 in second quadrant. 1st and second equations are directly deductible from the image, whereas the third is actually y = -x

Re: Which of the following is the equation of the line in the xy-plane tha [#permalink]

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30 Sep 2017, 00:12

mevicks wrote:

saiesta wrote:

Which of the following is the equation of the line in the xy-plane that has slope 0

(I) x = 2 (II) y = 3 (III) x + y = 0

A. I only B. II only C. III only D. I and II only E. II and III only

15 Second approach if you know how to visualize the lines spatially (Ron purewal method)

Basically anything parallel to Y axis has a slope undefined, parallel to X axis has slope 0, 45 Degrees has slope 1 in first quadrant, and 45 Degrees has slope -1 in second quadrant. 1st and second equations are directly deductible from the image, whereas the third is actually y = -x

Re: Which of the following is the equation of the line in the xy-plane tha [#permalink]

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15 Oct 2017, 04:40

yosita18 wrote:

saiesta wrote:

How can I tackle this question? The answer is B but I do not understand why? If the equation of a line is in the form y = mx + b. How could y = 3 have a slope of 0? Moreover, why can't statement I be the answer?

Quote:

My two cents: Which of the following is the equation of the line in the xy-plane that has slope 0

(I) x = 2 (II) y = 3 (III) x + y = 0

Consider the equation: y=mx+c ------------ Equation (1)

Now, given is that slope is 0, so, m=0 If you substitute in Equation (1), you get y=3 Now, y=3 is a horizontal line on the xy-plane, which has a slope ZERO. Also, consider x=2, x=2 is a vertical line, and slope of a vertical line is undefined, As the points on a vertical line would have same x-coordinate value. slope = m = (y2-y1)/(x2-x1) Option III, you have y=-x, so slope = -1.

Answer: B

Hi, I don't get the sentence marked in red above. How does substituting m=0 give y=3? It should give y=C. What am I missing here?