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NCERT Exemplar · Q57

Q.Match the entries of Column C1C_1 with their appropriate answers given under Column C2C_2. Column C1C_1:

(a) The coordinates of the points P and Q on the line x+5y=13x+5y=13 which are at a distance of 2 units from the line 12x−5y+26=012x-5y+26=0 are;
(b) The coordinates of the point on the line x+y=4x+y=4, which are at a unit distance from the line 4x+3y−10=04x+3y-10=0 are;
(c) The coordinates of the point on the line joining A(−2,5)(-2,5) and B(3,1)(3,1) such that AP == PQ == QB are. Column C2C_2:
(i) (3,1), (−7,11)(3,1),\,(-7,11);
(ii) (−13,113), (43,73)\left(-\dfrac{1}{3},\dfrac{11}{3}\right),\,\left(\dfrac{4}{3},\dfrac{7}{3}\right);
(iii) (1,125), (−3,165)\left(1,\dfrac{12}{5}\right),\,\left(-3,\dfrac{16}{5}\right).
Rajasthan RbseShort· 3mImportance★★★★★
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This problem involves finding points based on distance from a line and section formula; we find that (a) matches (iii), (b) matches (i), and (c) matches (ii).

Let's break down each part of the problem. Parts (a) and (b) rely on the concept of the distance from a point to a line, while part (c) uses the section formula.

Concept: Distance From a Point to a Line

The perpendicular distance from a point (x0,y0)(x_0, y_0) to a line given by the equation Ax+By+C=0Ax+By+C=0 is a fundamental concept in coordinate geometry. It represents the shortest distance between the point and any point on the line.

The distance dd from a point (x0,y0)(x_0, y_0) to a line Ax+By+C=0Ax+By+C=0 is given by:

d=∣Ax0+By0+C∣A2+B2d = \frac{|Ax_0+By_0+C|}{\sqrt{A^2+B^2}}

The absolute value in the numerator is crucial because distance is always non-negative. When we solve for coordinates, this absolute value will lead to two possible cases, corresponding to points on either side of the line (or in this problem, points on the given line that are at the specified distance from another line).

Concept: Section Formula

When a point divides a line segment joining two given points in a specific ratio, its coordinates can be found using the section formula.

If a point P(x,y)P(x,y) divides the line segment joining A(x1,y1)A(x_1, y_1) and B(x2,y2)B(x_2, y_2) internally in the ratio m:nm:n, then the coordinates of PP are:

P(x,y)=(nx1+mx2m+n,ny1+my2m+n)P(x,y) = \left(\frac{nx_1+mx_2}{m+n}, \frac{ny_1+my_2}{m+n}\right)

Now, let's solve each part.


Part (a): Finding points on x+5y=13x+5y=13 at a distance of 2 units from 12x−5y+26=012x-5y+26=0.

  1. Represent a general point on the first line:

    We are looking for points on the line x+5y=13x+5y=13. To simplify calculations, we can express one coordinate in terms of the other. From x+5y=13x+5y=13, we get x=13−5yx = 13-5y. So, any point on this line can be represented as (13−5y,y)(13-5y, y). Let's call this point (x0,y0)(x_0, y_0).

  2. Apply the distance formula:

    The distance from (x0,y0)=(13−5y,y)(x_0, y_0) = (13-5y, y) to the line 12x−5y+26=012x-5y+26=0 must be 2 units. Using the distance formula:

d=∣12(13−5y)−5y+26∣122+(−5)2d = \frac{|12(13-5y) - 5y + 26|}{\sqrt{12^2 + (-5)^2}}

We are given $d=2$, so:

2=∣156−60y−5y+26∣144+252 = \frac{|156 - 60y - 5y + 26|}{\sqrt{144 + 25}}

2=∣182−65y∣1692 = \frac{|182 - 65y|}{\sqrt{169}}

2=∣182−65y∣132 = \frac{|182 - 65y|}{13}

  1. Solve for yy using the absolute value: Multiplying by 13, we get:

∣182−65y∣=26|182 - 65y| = 26

This absolute value equation gives two possibilities:
*   **Case 1:** $182 - 65y = 26$
    $65y = 182 - 26$
    $65y = 156$
    $y = \frac{156}{65} = \frac{12 \times 13}{5 \times 13} = \frac{12}{5}$
*   **Case 2:** $182 - 65y = -26$
    $65y = 182 + 26$
    $65y = 208$
    $y = \frac{208}{65} = \frac{16 \times 13}{5 \times 13} = \frac{16}{5}$

4. Find the corresponding xx coordinates:

Using x=13−5yx = 13-5y:

* For y=125y = \frac{12}{5}:

x=13−5(125)=13−12=1x = 13 - 5\left(\frac{12}{5}\right) = 13 - 12 = 1

This gives the point (1,125)\left(1, \frac{12}{5}\right).

* For y=165y = \frac{16}{5}:

x=13−5(165)=13−16=−3x = 13 - 5\left(\frac{16}{5}\right) = 13 - 16 = -3

This gives the point (−3,165)\left(-3, \frac{16}{5}\right).

These are the two points P and Q.
Comparing with Column $C_2$, these points match option (iii).

Part (b): Finding points on x+y=4x+y=4 at a unit distance from 4x+3y−10=04x+3y-10=0.

  1. Represent a general point on the first line:

    For the line x+y=4x+y=4, we can write x=4−yx = 4-y. So, any point on this line is (4−y,y)(4-y, y). Let this be (x0,y0)(x_0, y_0).

  2. Apply the distance formula:

    The distance from (x0,y0)=(4−y,y)(x_0, y_0) = (4-y, y) to the line 4x+3y−10=04x+3y-10=0 must be 1 unit.

d=∣4(4−y)+3y−10∣42+32d = \frac{|4(4-y) + 3y - 10|}{\sqrt{4^2 + 3^2}}

Given $d=1$:

1=∣16−4y+3y−10∣16+91 = \frac{|16 - 4y + 3y - 10|}{\sqrt{16 + 9}}

1=∣6−y∣251 = \frac{|6 - y|}{\sqrt{25}}

1=∣6−y∣51 = \frac{|6 - y|}{5}

  1. Solve for yy using the absolute value: Multiplying by 5:

∣6−y∣=5|6 - y| = 5

Again, two possibilities:
*   **Case 1:** $6 - y = 5$
    $y = 6 - 5 = 1$
*   **Case 2:** $6 - y = -5$ …

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