Partitioning Line Segments via Ratio

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Geometry › Partitioning Line Segments via Ratio

Questions 1 - 10
1

In the coordinate plane shown, segment $\overline{AB}$ has endpoints $A(1,-3)$ and $B(9,5)$. Point $P$ divides the directed segment from $A$ to $B$ internally so that $AP:PB=3:1$. Which coordinates represent the partition point?

$(5,1)$

$(3,-1)$

$(10,6)$

$(7,3)$

Explanation

The skill is partitioning a line segment in a given ratio. The endpoints are A(1,-3) and B(9,5), with the ratio AP:PB = 3:1. This means point P is a weighted average where A has weight 1 and B has weight 3, since the weights are the opposite parts of the ratio. Applying the ratio, the coordinates are x = (11 + 39)/4 = 28/4 = 7 and y = (1*(-3) + 3*5)/4 = 12/4 = 3, so P is at (7,3). This result is justified because it positions P three-fourths of the way from A to B, consistent with the ratio 3:1. A common distractor misconception is using the midpoint, leading to (5,1), which ignores the unequal ratio. To transfer this strategy, think in terms of weights, not distances.

2

On the coordinate plane, points $A(-4,1)$ and $B(2,7)$ are connected by segment $\overline{AB}$. Point $P$ lies on the directed segment from $A$ to $B$ and divides $\overline{AB}$ internally in the ratio $AP:PB=1:2$. Which point divides the segment in the given ratio?

$(-1,2)$

$(0,5)$

$(-6,-1)$

$(-2,3)$

Explanation

The skill is partitioning a line segment in a given ratio. The endpoints are A(-4,1) and B(2,7), with the ratio AP:PB = 1:2. This means point P is a weighted average where A has weight 2 and B has weight 1, since the weights are the opposite parts of the ratio. Applying the ratio, the coordinates are x = (2*(-4) + 12)/3 = -6/3 = -2 and y = (21 + 1*7)/3 = 9/3 = 3, so P is at (-2,3). This result is justified because it positions P one-third of the way from A to B, consistent with the ratio 1:2. A common distractor misconception is reversing the ratio to 2:1, leading to (0,5), which assumes the larger part is toward A instead of B. To transfer this strategy, think in terms of weights, not distances.

3

In the coordinate plane, endpoints are $A(-3,6)$ and $B(9,0)$. Which coordinates represent the point $P$ that divides $\overline{AB}$ internally in the ratio $AP:PB=5:1$?

$(7,1)$

$(6,2)$

$(5,3)$

$(8,0)$

Explanation

This problem asks for point P that divides segment AB internally where A(-3,6) and B(9,0) with ratio AP:PB = 5:1. The endpoints are A(-3,6) and B(9,0), and P partitions the segment so that AP is 5 parts while PB is 1 part. Using the section formula with weighted averages, P = ((1·A + 5·B)/(5+1)), where we weight by opposite ratio parts. Calculating: P = ((1·(-3,6) + 5·(9,0))/6) = ((-3,6) + (45,0))/6 = (42,6)/6 = (7,1). This result is logical since P is very close to B, being 5/6 of the way from A to B. A typical mistake would be to use the ratio parts directly as weights, which would incorrectly place P near A. The key insight is that larger opposite weights pull the point toward that endpoint, so we weight B more heavily since P is closer to B.

4

On the coordinate plane, segment $\overline{AB}$ has endpoints $A(0,2)$ and $B(8,-6)$. Point $P$ divides the directed segment from $A$ to $B$ internally in the ratio $AP:PB=5:3$. Which coordinates represent the partition point?

$(4,-2)$

$(5,-3)$

$(3,-1)$

$(10,-8)$

Explanation

The skill is partitioning a line segment in a given ratio. The endpoints are A(0,2) and B(8,-6), with the ratio AP:PB = 5:3. This means point P is a weighted average where A has weight 3 and B has weight 5, since the weights are the opposite parts of the ratio. Applying the ratio, the coordinates are x = (30 + 58)/8 = 40/8 = 5 and y = (32 + 5(-6))/8 = -24/8 = -3, so P is at (5,-3). This result is justified because it positions P five-eighths of the way from A to B, consistent with the ratio 5:3. A common distractor misconception is misapplying the weights, leading to (4,-2) by incorrectly averaging without proper ratio consideration. To transfer this strategy, think in terms of weights, not distances.

5

Points $N(-1,0)$ and $O(7,8)$ are plotted on a coordinate plane and connected by segment $\overline{NO}$. Point $V$ divides the directed segment from $N$ to $O$ internally in the ratio $NV:VO=5:3$. Which coordinates represent the partition point $V$?

$(4,5)$

$(2,3)$

$(5,6)$

$(3,4)$

Explanation

The skill here is partitioning a line segment in a given ratio using the section formula. The endpoints are N(-1,0) and O(7,8), with the ratio NV:VO = 5:3. This means point V is a weighted average of N and O, where the weight for N is 3 and for O is 5, because the weights are the ratios of the opposite segments. Applying the formula, the coordinates of V are ((5·7 + 3·(-1))/(5+3), (5·8 + 3·0)/(5+3)) = (4, 5). This result is justified because it places V such that the segment is divided into 5 parts from N to V and 3 parts from V to O, totaling 8 parts. A common distractor misconception is using equal weights, leading to the midpoint (3,4). To transfer this strategy, think in terms of weights assigned to each endpoint rather than direct distances.

6

In the coordinate plane, segment $\overline{AB}$ has endpoints $A(2,5)$ and $B(8,-1)$. Which point divides the directed segment $\overrightarrow{AB}$ internally in the ratio $AP:PB=1:2$?

$(4,3)$

$(6,1)$

$(5,2)$

$(3,4)$

Explanation

This problem requires finding point P that partitions segment AB where A(2,5) and B(8,-1) in the ratio AP:PB = 1:2. The endpoints are A(2,5) and B(8,-1), and P divides the segment so that AP is 1 part while PB is 2 parts of the total distance. Using the weighted average approach, we weight each endpoint by the opposite ratio part: P = ((2·A + 1·B)/(1+2)). Applying this formula: P = ((2·(2,5) + 1·(8,-1))/3) = ((4,10) + (8,-1))/3 = (12,9)/3 = (4,3). This result makes sense because P is closer to A than to B, being 1/3 of the way from A to B. A common mistake would be to weight A by 1 and B by 2, which would incorrectly place P closer to B. The key strategy is to remember that in weighted averages, larger weights pull the result closer to that point, so we use opposite ratio parts.

7

Points $A(0,0)$ and $B(10,5)$ are plotted on the coordinate plane. Which point divides the directed segment $\overrightarrow{AB}$ internally in the ratio $AP:PB=3:7$?

$(3,2)$

$(7,4)$

$(3,1.5)$

$(5,2.5)$

Explanation

This problem requires finding point P that partitions segment AB where A(0,0) and B(10,5) in the ratio AP:PB = 3:7. The endpoints are A(0,0) and B(10,5), with P dividing the segment such that AP is 3 parts and PB is 7 parts of the total distance. Using the weighted average approach, P = ((7·A + 3·B)/(3+7)), weighting each endpoint by the opposite ratio part. Applying this: P = ((7·(0,0) + 3·(10,5))/10) = ((0,0) + (30,15))/10 = (30,15)/10 = (3,1.5). Since P is 3/10 of the way from A to B, it's much closer to A than to B, which matches our result. A common misconception would be to weight A by 3 and B by 7, incorrectly placing P closer to B. The transfer strategy is to visualize the ratio as weights in a balance, where opposite weights determine the equilibrium point.

8

Point $$P$$ is located at $$(-4, 7)$$ and point $$Q$$ is located at $$(8, -5)$$. If point $$R$$ divides segment $$\overline{PQ}$$ in the ratio $$2:1$$ from $$P$$ to $$Q$$, and then point $$S$$ divides segment $$\overline{PR}$$ in the ratio $$1:2$$ from $$P$$ to $$R$$, what are the coordinates of point $$S$$?

$$(0, 3)$$

$$(-1, 5)$$

$$(4, -1)$$

$$(2, 1)$$

Explanation

First, find point R that divides PQ in ratio 2:1. Using the section formula: R = P + (2/3)(Q - P) = (-4, 7) + (2/3)((8, -5) - (-4, 7)) = (-4, 7) + (2/3)(12, -12) = (-4, 7) + (8, -8) = (4, -1). Next, find point S that divides PR in ratio 1:2. S = P + (1/3)(R - P) = (-4, 7) + (1/3)((4, -1) - (-4, 7)) = (-4, 7) + (1/3)(8, -8) = (-4, 7) + (8/3, -8/3) = (0, 3). Choice B incorrectly uses the wrong ratio for the second partition. Choice C results from switching the direction of one of the ratios. Choice D gives the coordinates of point R instead of point S.

9

A directed line segment from point $$X(-6, 4)$$ to point $$Y(9, -2)$$ is partitioned by point $$Z$$ such that $$\overline{XZ} : \overline{ZY} = m : n$$ where $$m$$ and $$n$$ are positive integers. If the $$x$$-coordinate of point $$Z$$ is $$3$$, what is the value of $$\frac{m}{n}$$?

$$\frac{2}{3}$$

$$\frac{3}{2}$$

$$\frac{3}{5}$$

$$\frac{5}{3}$$

Explanation

Using the section formula, if Z partitions XY in ratio m:n, then Z = (nX + mY)/(m + n). For the x-coordinate: 3 = (n(-6) + m(9))/(m + n) = (-6n + 9m)/(m + n). Cross-multiplying: 3(m + n) = -6n + 9m, so 3m + 3n = -6n + 9m, which gives 9n = 6m, or m/n = 9/6 = 3/2. Choice A reverses the ratio. Choice C would result from incorrectly setting up the equation. Choice D results from confusing which segment corresponds to which part of the ratio.

10

On the coordinate plane, points $L(-4,-1)$ and $M(2,5)$ are connected by segment $\overline{LM}$. Which point divides the directed segment from $L$ to $M$ internally in the ratio $LP:PM=1:2$?

$(-1,2)$

$(-3,0)$

$(0,3)$

$(-2,1)$

Explanation

The skill involves partitioning a line segment in a given ratio using coordinates. Here, the endpoints are L(-4,-1) and M(2,5), and the ratio LP:PM is 1:2. The point P is a weighted average of the coordinates of L and M, with weights corresponding to the opposite segments: weight 2 for L and 1 for M. Thus, x = (2*(-4) + 12)/(1+2) = (-8 + 2)/3 = -6/3 = -2, and y = (2(-1) + 1*5)/3 = (-2 + 5)/3 = 3/3 = 1, so P is (-2,1). This result places P such that it divides the segment with LP being 1/3 and PM being 2/3 of the total length, satisfying the ratio. A common distractor misconception is swapping to 2:1, leading to (0,3), which is choice B. Transfer strategy: think in terms of weights, not distances.

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