Coordinate Geometry | Exercise 7.1

Question 7

Find the point on the xx-axis which is equidistant from (2,5)(2, -5) and (2,9)(-2, 9).

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Solution

Equidistant: A point is equidistant from two other points if its distance from both is exactly equal. Any point on the x-axis has coordinates (x,0)(x, 0) since its y-coordinate is always 0.

Distance Formula: The distance between two points A(x1,y1)\text{A}(x_1, y_1) and B(x2,y2)\text{B}(x_2, y_2):

d=(x2x1)2+(y2y1)2d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}

We use the distance formula to find the point on the x-axis that is equally far from the two given points.

Step 1 — Set up the problem

Let's call the two given points A(2,-5)\text{A}(\textbf{2}, \textbf{-5}) and B(-2,9)\text{B}(\textbf{-2}, \textbf{9}). We need to find a point on the x-axis. Any point on the x-axis has its y-coordinate as 0\textbf{0}. So, let's call this point P(x,0)\text{P}(x, \textbf{0}). The problem states that point P\text{P} is equidistant from A\text{A} and B\text{B}. This means the distance PA\text{PA} must be equal to the distance PB\text{PB}. We will use the distance formula: d=(x2x1)2+(y2y1)2d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}.

PA=(2x)2+(50)2PA = \sqrt{(2 - x)^2 + (-5 - 0)^2}

PB=(2x)2+(90)2PB = \sqrt{(-2 - x)^2 + (9 - 0)^2}

Since PA=PB\text{PA} = \text{PB}, we can write:

(2x)2+(5)2=(2x)2+(9)2\sqrt{(2 - x)^2 + (-5)^2} = \sqrt{(-2 - x)^2 + (9)^2}

Step 2 — Solve for x

To get rid of the square roots, we can square both sides of the equation.

(2x)2+(5)2=(2x)2+(9)2(2 - x)^2 + (-5)^2 = (-2 - x)^2 + (9)^2

Let's expand the squared terms.

(44x+x2)+25=(4+4x+x2)+81(4 - 4x + x^2) + 25 = (4 + 4x + x^2) + 81

Now, we can simplify both sides of the equation.

x24x+29=x2+4x+85x^2 - 4x + 29 = x^2 + 4x + 85

We can subtract x2x^2 from both sides.

4x+29=4x+85-4x + 29 = 4x + 85

Let's gather the xx terms on one side and constant terms on the other.

2985=4x+4x29 - 85 = 4x + 4x

56=8x-56 = 8x

Finally, we solve for xx.

x=568x = \frac{-56}{8}

x=7x = -7

So, the x-coordinate of point P\text{P} is -7\textbf{-7}. The point on the x-axis is P(-7,0)\text{P}(\textbf{-7}, \textbf{0}).

P(7,0)\boxed{P(-7, 0)}

Answer

The point on the x-axis equidistant from (2,5)(2, -5) and (2,9)(-2, 9) is (7,0)(-7, 0).

More questions in Exercise 7.1

Q1

Find the distance between the following pairs of points :

(i) (2,3),(4,1)(2, 3), (4, 1) (ii) (5,7),(1,3)(-5, 7), (-1, 3) (iii) (a,b),(a,b)(a, b), (-a, -b)

Q2

Find the distance between the points (0,0)(0, 0) and (36,15)(36, 15). Can you now find the distance between the two towns A and B discussed in Section 7.2.

Q3

Determine if the points (1,5),(2,3)(1, 5), (2, 3) and (2,11)(-2, -11) are collinear.

Q4

Check whether (5,2),(6,4)(5, -2), (6, 4) and (7,2)(7, -2) are the vertices of an isosceles triangle.

Q5

In a classroom, 4 friends are seated at the points A, B, C and D as shown in Fig. 7.8. Champa and Chameli walk into the class and after observing for a few minutes Champa asks Chameli, “Don’t you think ABCD is a square?” Chameli disagrees. Using distance formula, find which of them is correct.

Q6

Name the type of quadrilateral formed, if any, by the following points, and give reasons for your answer:

(i) (1,2),(1,0),(1,2),(3,0)(-1, -2), (1, 0), (-1, 2), (-3, 0)

(ii) (3,5),(3,1),(0,3),(1,4)(-3, 5), (3, 1), (0, 3), (-1, -4)

(iii) (4,5),(7,6),(4,3),(1,2)(4, 5), (7, 6), (4, 3), (1, 2)

Q7

Find the point on the xx-axis which is equidistant from (2,5)(2, -5) and (2,9)(-2, 9).

Q8

Find the values of yy for which the distance between the points P(2,3)P(2, -3) and Q(10,y)Q(10, y) is 10 units.

Q9

If Q(0, 1) is equidistant from P(5, –3) and R(x, 6), find the values of x. Also find the distances QR and PR.

Q10

Find a relation between x and y such that the point (x, y) is equidistant from the point (3, 6) and (–3, 4).

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