Given the points A(-1,2) and B(7,8), find the coordinates of the point P on directed line segment AB that partitions AB in the ratio 1:3
A. (1, 7/2)B. (3,5)C.(5, 13/2)D. (7,8)

Respuesta :

Now despite what you may believe, 1:3 is not 1/3 in this situation. In this case, it means "1 equal part to 3 equal parts", which is a total of 4 equal parts. In short, this question is to place point P 1/4 the distance from A to B.

Firstly, how far apart is -1 from 7 (the x-coordinates)? That would be 8 units. Multiply 1/4 by 8:

[tex]\frac{1}{4}\times \frac{8}{1}=\frac{8}{4}=2[/tex]

Next, how far apart is 2 from 8 (the y-coordinates)? That would be 6 units. Multiply 1/4 by 6:

[tex]\frac{1}{4}\times \frac{6}{1}=\frac{6}{4}=\frac{3}{2}[/tex]

Next, since from -1 to 7 you are increasing, add 2 to -1:

[tex]-1+2=1[/tex]

1 is your x-coordinate

Next, since from 2 to 8 you are increasing, add 3/2 to 2:

[tex]\frac{2}{1}\times \frac{2}{2}=\frac{4}{2}\\\\\frac{4}{2}+\frac{3}{2}=\frac{7}{2}[/tex]

7/2 is your y-coordinate.

Putting it together, your answer is A. (1, 7/2)

We need to find the coordinate that divides the line AB in the ratio 1:3.

The point P lies in A. [tex]\left(1,\dfrac{7}{2}\right)[/tex].

The points of the line are

[tex]A(-1,2)[/tex] and [tex]B(7,8)[/tex]

The ratio of division is [tex]m:n=1:3[/tex]

The formula for partitioning is

[tex]P=\left(\dfrac{mx_2+nx_1}{m+n},\dfrac{my_2+ny_1}{m+n}\right)\\\Rightarrow P=\left(\dfrac{1\times 7+3\times-1}{1+3},\dfrac{1\times 8+3\times 2}{1+3}\right)\\\Rightarrow P=\left(\dfrac{7-3}{4},\dfrac{8+6}{4}\right)\\\Rightarrow P=\left(1,\dfrac{7}{2}\right)[/tex]

So, the point P lies in A. [tex]\left(1,\dfrac{7}{2}\right)[/tex].

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