Coordinate Geometry | Exercise 7.1

Question 4

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

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Solution

Isosceles Triangle: A triangle is called isosceles if exactly two of its three sides are equal in length. To verify, we calculate the distance between each pair of points and check if at least two distances are equal.

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) is given by:

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

We will use the distance formula to find the length of each side of the triangle.

Step 1 — Calculate the length of side AB

Let's label the given points as A(5,2\mathbf{5, -2}), B(6,4\mathbf{6, 4}), and C(7,2\mathbf{7, -2}). We use the distance formula: ((x2x1)2+(y2y1)2)\sqrt{((x_2 - x_1)^2 + (y_2 - y_1)^2)}.

AB=((65)2+(4(2))2)AB = \sqrt{((6 - 5)^2 + (4 - (-2))^2)}

=((1)2+(4+2)2)= \sqrt{((1)^2 + (4 + 2)^2)}

=(12+62)= \sqrt{(1^2 + 6^2)}

=(1+36)= \sqrt{(1 + 36)}

AB=37 units\boxed{AB = \sqrt{37} \text{ units}}

Diagram 1

Step 2 — Calculate the length of side BC

Now, let's find the distance between points B(6,4\mathbf{6, 4}) and C(7,2\mathbf{7, -2}). We apply the distance formula again.

BC=((76)2+(24)2)BC = \sqrt{((7 - 6)^2 + (-2 - 4)^2)}

=((1)2+(6)2)= \sqrt{((1)^2 + (-6)^2)}

=(1+36)= \sqrt{(1 + 36)}

BC=37 units\boxed{BC = \sqrt{37} \text{ units}}

Step 3 — Calculate the length of side CA

Next, we find the distance between points C(7,2\mathbf{7, -2}) and A(5,2\mathbf{5, -2}). We use the distance formula one more time.

CA=((57)2+(2(2))2)CA = \sqrt{((5 - 7)^2 + (-2 - (-2))^2)}

=((2)2+(2+2)2)= \sqrt{((-2)^2 + (-2 + 2)^2)}

=((2)2+(0)2)= \sqrt{((-2)^2 + (0)^2)}

=(4+0)= \sqrt{(4 + 0)}

=4= \sqrt{4}

CA=2 units\boxed{CA = 2 \text{ units}}

Step 4 — Check if it is an isosceles triangle

We compare the lengths of the three sides we found. We have AB=37AB = \sqrt{37} units, BC=37BC = \sqrt{37} units, and CA=2CA = 2 units. An isosceles triangle has at least two sides of equal length. Here, we see that AB=BCAB = BC. Since two sides are equal, the triangle is isosceles.

Answer

Yes, the points (5,2)\mathbf{(5, -2)}, (6,4)\mathbf{(6, 4)} and (7,2)\mathbf{(7, -2)} are the vertices of an isosceles triangle.

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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