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In summary: AB and BC)In summary, external division of a line segment results in a negative ratio due to the direction of the vectors involved. The correct formula to use for external division is x = (mx2+nx1)/(m+n) and the ratio of distance can be negative when direction is taken into account.
- #1
parshyaa
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Whats the difference between (4/3) and -(4/3)
Why ratio in external division is negative?
I have answer for how it is negative but not why?
X = (mx2+nx1)/(m+n)
⇒ (mx2+nx1) = X(m+n)
⇒m(x2-X) = n(X-x1)
⇒(m/n) = (X-x1)/(x2-X)
From the above equation we can conclude that when division is external then X must be greater than x1 and x2, therefore ratio becomes negative
But what's the purpose of negative ratio.
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- #2
hilbert2
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A ratio is negative when the divisor and dividend are of different sign.
- #3
parshyaa
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hilbert2 said:
A ratio is negative when the divisor and dividend are of different sign.
Distance can never be negative then why external division gives negative ratio.
- #4
hilbert2
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You can't calculate a positive definite distance without having an absolute value expression ##|x_1 - x_2 |## or a Pythagorean type formula that has squares inside a square root.
- #5
mfb
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What do you mean by "external" division? Divisions have a numerator and a denominator. If their signs are different, the result of the division is negative.
parshyaa said:
If X>x2 and X>x1, then either m or n has to be negative. So what?
- #6
parshyaa
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mfb said:
What do you mean by "external" division? Divisions have a numerator and a denominator. If their signs are different, the result of the division is negative.If X>x2 and X>x1, then either m or n has to be negative. So what?
In my above example there are 3 points let us name them P(x1,y1), Q(x2,y2), and let a point R(X,Y) lies between P and Q and divides PQ in the ratio PR/QR = m/n, as given in diagram.
Here R divides PQ internally in the ratio (m/n) when R goes along PQ then it divides PQ externally in the ratio m/n, but when it goes along PQ its cordinate X becomes greater than x1& x2, and y becomes greater than y1 & y2, and by using my above reasoning we get to know that m/n becomes negative, how can the ratio of distance become negative
- #7
FactChecker
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In your diagram, (m/n) = (X-x1)/(x2-X) is arranged so that it is positive as long as R is between P and Q. The "distances" X-x1 and x2-X are really vectors, not distances, because the direction counts. As soon as R goes outside of the [P,Q] segment, one of the directions changes and the ratio becomes negative.
- #8
Buffu
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You are using wrong formula, the right one is ##x = {mx_2 - nx_1 \over m -n}##. The rest is explained by fact checker.
- #9
parshyaa
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Buffu said:
You are using wrong formula, the right one is ##x = {mx_2 - nx_1 \over m -n}##. The rest is explained by fact checker.
Hey i know that this is the formua for external division, but i used the above formula to show that how ratio m/n becomes negative when point R goes along PQ and divides PQ externally. By using your formula we can't show that m/n is negative, check it.
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Buffu
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parshyaa said:
Hey i know that this is the formua for external division, but i used the above formula to show that how ratio m/n becomes negative when point R goes along PQ and divides PQ externally. By using your formula we can't show that m/n is negative, check it.
Why do you want to show m/n is negative purposely ?
- #12
parshyaa
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Buffu said:
Why do you want to show m/n is negative purposely ?
Hey that's not purposely, m/n is always negative in external divison of line, just read the concept
- #13
FactChecker
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There are better ratios to use that are useful for interpolating between the endpoints and also for extrapolating beyond the endpoints.
- #14
Buffu
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parshyaa said:
Hey that's not purposely, m/n is always negative in external divison of line, just read the concept
It is negative because you need to use the correct formula not the wrong one.
For a ratio (-m/n), the division is ##-mx_2 + nx_1 \over n - m## compare it with ##x_1n - mx_2\over n -m##(I applied the formula for m/n).
Both are same thing, you are just creating a fuss over nothing.
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- #15
parshyaa
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Buffu said:
For a ratio (-m/n), the division is ##-mx_2 + nx_1 \over n - m## compare it with ##x_1n - mx_2\over n -m##
How can you take ratio of two distance as (-m/n) and substitute in the formula, ratio of distance can't be negative.
- #16
Svein
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parshyaa said:
How can you take ratio of two distance as (-m/n) and substitute in the formula, ratio of distance can't be negative.
Why not?
- #17
parshyaa
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Svein said:
Why not?
How can you divide a line in the ratio -(4/3)
- #18
Buffu
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parshyaa said:
How can you divide a line in the ratio -(4/3)
Yes you can.
Direction matters. When you write ##m/n## it means you are preserving the direction. To only account for distance you should write ##|m/n|## and then tell explicitly what you need to do with this ratio (divide the segment externally or internally) and then use the correct formula accordingly (See the derivation of those formulae). The benefit in writing ##m/n## is that you don't need to worry about that extra bit of information (nature of division) explicitly.
Isn't this what @FactChecker said ?
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- #19
Ray1733
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Look ...it's important to understand what section formula actually has to say...
When we say c divides AB vector then it actually means that (AC vector)/(CB vector)=k (some constant)
As a,b,c are collinear points,the k is a constant...according to collinear dependency
Now,for internal division it becomes positive as numerator and denominator (vectors) have same direction...and then by similar argument, the ration for external division will be negetive as the vectors will have opposite direction on same support
What does negative ratio mean in mathematics?
A negative ratio in mathematics refers to a relationship between two quantities where one quantity decreases while the other quantity increases. This is represented by a negative number in front of the ratio, such as -2:3.
How is a negative ratio different from a positive ratio?
A negative ratio is different from a positive ratio in that a positive ratio indicates a direct relationship between two quantities, where both quantities increase or decrease together. In contrast, a negative ratio indicates an inverse relationship, where one quantity increases while the other decreases.
Can a negative ratio be simplified?
Yes, a negative ratio can be simplified just like a positive ratio. To simplify a negative ratio, divide both numbers by their greatest common factor, and keep the negative sign in front of the ratio. For example, -4:8 can be simplified to -1:2.
Can a negative ratio be written as a decimal or fraction?
Yes, a negative ratio can be written as a decimal or fraction. To convert a negative ratio to a decimal, divide the first number by the second number. For example, -2:3 can be written as -0.67. To convert a negative ratio to a fraction, write the first number as the numerator and the second number as the denominator. For example, -2:3 can be written as -2/3.
What are some real-life examples of negative ratios?
Some real-life examples of negative ratios include the relationship between time and distance for a car traveling in reverse, the ratio of loss to gain in a stock market, and the ratio of decrease in the number of trees to the increase in pollution in a certain area.
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