Solving Problem with Circles in Backyard: Center (1,-1.5), Radius sqrt(29.25)

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Homework Help Overview

The problem involves finding the equation of the locus of a cat walking in a backyard, where the cat's position is defined by its perpendicular distances to two trees located at specific grid points. The subject area pertains to geometry and coordinate systems, particularly involving circles and loci.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to derive the equation of a circle based on the geometric relationship between the cat and the trees. Some participants question the accuracy of the calculations and the derived equation, while others confirm the correctness of the final expression.

Discussion Status

The discussion has seen participants verifying calculations and addressing typographical errors. There is a mix of uncertainty and affirmation regarding the correctness of the derived equation, with some participants suggesting that the original poster's final answer is indeed correct.

Contextual Notes

Participants note the presence of a typo in the calculations, which has been acknowledged and corrected. There is an ongoing exploration of the implications of the geometric setup and the relationships involved.

Imperil
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In a backyard, there are two trees located at grid points A(-2, 3) and B(4, -6). The family cat is walking in the backyard. The line segments between the cat and the two trees are always perpendicular. Find the equation of the locus of the cat.

My Answer:

slope PA = (y - 3) / (x + 2)
slope PB = (y + 6) / (x - 4)
slope PA = -1 / slope PB (since the lines between PA and PB are perpendicular)

(y - 3) / (x + 2) = -1 / [(y + 6) / (x - 4)]
(y - 3) / (x + 2) = -1 * (x - 4) / (y + 6)
(y - 3) / (x + 2) = (-x+4) / (y + 6)

(y - 3) (y + 6) = (x + 2)(-x + 4)
y^2 + 3y - 18 = -x^2 + 2x + 8
x^2 + y^2 - 2x + 3y - 26 = 0

x^2 - 2x + 1 + y^2 + 3y + 2.25 = 26 + 1 + 2.25
(x - 1)^2 + (y + 1.5)^2 = 29.25

Therefore the cat is walking in a circle with center (1, -1.5) and radius sqrt(29.25).

I believe that my answer is incorrect but is there something I am missing? I have tried doing this question multiple times and I still can't find the correct answer.

EDIT: corrected a typo
 
Last edited:
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Imperil said:
(y - 3) (y + 6) = (x + 2)(-x + 4)
y^2 + 3y - 18 = -x^2 + 2x + 8
x^2 + y^2 - 2x + 3y - 10 = 0

-18 - 8 = -26, not -10.
 
Sorry yes that was a typo from a mistake I made on an old page.

I just checked by using x = 1 for a point on the circle and I believe that my answer is correct the way I have it (I edited the mistake)? I just tested with x=1 point on the circle and the lines now seem to be perpendicular
 
Yes, your answer is correct.
 
Thanks so much dx I really appreciate your time :)
 

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