MHB How do I find the most efficient way to find P?

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To find point P given points B=(5,21), C=(40,-14), and the ratio $\frac{BP}{PC}=1/6$, the most efficient method involves using the section formula. The coordinates of P can be calculated as P=(6/7)B+(1/7)C, which means P is positioned 1/7 of the way from B to C. The calculations yield P at (10,16) by determining the x and y coordinates based on the specified ratio. The discussion also highlights the importance of clearly stating conditions in mathematical problems for accurate solutions. Understanding the concept of the locus defined by the ratio is crucial for solving similar problems.
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Let B=(5,21), C=(40,-14) and $\frac{BP}{PC}$=1/6. What is the most efficent way to find P? My book just states P=(6/7)B+(1/7)C but no idea how they got that.
 
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Poirot said:
Let B=(5,21), C=(40,-14) and $\frac{BP}{PC}$=1/6. What is the most efficent way to find P? My book just states P=(6/7)B+(1/7)C but no idea how they got that.

Draw a sketch.
 

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Poirot said:
Let B=(5,21), C=(40,-14) and $\frac{BP}{PC}$=1/6. What is the most efficent way to find P? My book just states P=(6/7)B+(1/7)C but no idea how they got that.

If x and y are the coordinates of P, then it must be...

$\displaystyle f(x,y)= 36\ (x-5)^{2} + 36\ (y-21)^{2} - (x-40)^{2} - (y+14)^{2}=0$ (1)

The (1) is a 'quadratic curve' as illustrated in...

Quadratic Curve -- from Wolfram MathWorld

Kind regards

$\chi$ $\sigma$
 

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Hello, Poirot!

Did you make a sketch?

Let $B=(5,21),\;C=(40,\text{-}14),\;\dfrac{BP}{PC}=\dfrac{1}{6}$

What is the most efficent way to find $P$ ?
Code:
      |
      | (5,21)   +35
      |  B♥ → → → → → → +
      |     *           ↓
      |      Po         ↓
      |         *       ↓ -35
  ----+-----------*-----↓------
      |             *   ↓
      |               * ↓
      |                 ♥C
      |              (40,-14)
      |
Going from $B$ to $C$, we move 35 right and 35 down.

Point $P$ is $\tfrac{1}{7}$ of the way from $B$ to $C$.

The x-coordinate is $\tfrac{1}{7}$ of the way from $5$ to $40$.
. . Hence: .$x \;=\;5 + \tfrac{1}{7}(40-5) \;=\;5 + \tfrac{1}{7}(35) \;=\;5 + 5 \;=\;10$

The y-coordinate is $\tfrac{1}{7}$ of the way from $21$ to $\text{-}14.$
. . Hence: .$y \;=\;21 + \tfrac{1}{7}(\text{-}14 - 21) \;=\;21 + \tfrac{1}{7}(\text{-}35) \;=\;21 - 5 \;=\;16$Therefore, $P$ is at $(10,16).$
 
Poirot said:
Let B=(5,21), C=(40,-14) and $\frac{BP}{PC}$=1/6. What is the most efficent way to find P? My book just states P=(6/7)B+(1/7)C but no idea how they got that.

If your book gives that answer then you have not posted the question as asked, or omitted implied side conditions for the question set.

The quoted answer implies that you want a point P between B and C, while the statement does not so constrain P and defines a locus in the plane.

In future please post the question as asked and include any additional constraints implied by the topic you are studying and or the common conditions in force on a question set.

CB
 
I've solved this now thanks to the answers.
 

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