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NCERT Exemplar · Class 10 · Maths

Chapter 7: Coordinate Geometry

Practice each question, then open the answer or worked solution.

Exercise 7.4

3 questions
Q1Written answer

If (– 4, 3) and (4, 3) are two vertices of an equilateral triangle, find the coordinates of the third vertex, given that the origin lies in the interior of the triangle.

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Worked solution

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 1

Let the vertices be (x,y)

Distance between (x,y) & (4,3) is = √((x-4)2 + (y-3)2)……(1)

Distance between (x,y) & (-4,3) is = √((x+4)2 + (y-3)2)……(2)

Distance between (4,3) &(-4,3) is =√((4+4)2 + (3-3)2) = √(8)²=8

According to the question,

Equation (1)=(2)

(x-4)²=(x+4)²

x²-8x+16=x²+8x+16

16x=0

x=0

Also, equation (1)=8

(x-4)²+(y-3)²=64……… (3)

Substituting the value of x in (3)

Then (0-4)²+(y-3)²=64

(y-3)²=64-16

(y-3)²=48

y-3=(+)4√3

y=3(+) 4√3

Neglect y = 3+4√3 as if y = 3+4√3 then origin cannot interior of triangle

Therefore, the third vertex = (0, 3-4√3)

Q2Written answer

A (6, 1), B (8, 2) and C (9, 4) are three vertices of a parallelogram ABCD. If E is the midpoint of DC, find the area of △ ADE.

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Worked solution

According to the question,

The three vertices of a parallelogram ABCD are A (6, 1), B (8, 2) and C (9, 4)

Let the fourth vertex of parallelogram = (x, y),

We know that, diagonals of a parallelogram bisect each other

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 2

Since, mid – point of a line segment joining the points (x1, y1) and (x2, y2) is given by,

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 2-1

∵ Area of ΔABC with vertices (x1, y1), (x2, y2) and (x3, y3);

= ½[x1(y2 – y3) + x2(y3 – y1) + x3(y1 – y2)]

∴ Area of ΔADE with vertices A (6, 1), D (7, 3) and E (8, (7/2))

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 2-2

= – ¾ but area can’t be negative

Hence, the required area of ΔADE is ¾ sq. units

Q3Written answer

The points A (x1, y1), B (x2, y2) and C (x3 y3) are the vertices of ABC.

(i) The median from A meets BC at D. Find the coordinates of the point D.

(ii) Find the coordinates of the point P on AD such that AP : PD = 2 : 1

(iii) Find the coordinates of points Q and R on medians BE and CF, respectively such that BQ : QE = 2 : 1 and CR : RF = 2 : 1

(iv) What are the coordinates of the centroid of the triangle ABC?

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Worked solution

According to the question,

The vertices of ΔABC = A, B and C

Coordinates of A, B and C = A(x1, y1), B(x2, y2), C(x3, y3)

(i) As per given information D is the mid – point of BC and it bisect the line into two equal parts.

Coordinates of the mid – point of BC;

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 3-1

(ii) Let the coordinates of a point P be (x, y)

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 3-2

Given,

The ratio in which the point P(x, y), divide the line joining,

A(x1, y1) and D((x2+x3)/2 , (y2+y3)/2)) = 2:1

Then,

Coordinates of P =

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 3-2

(iii) Let the coordinates of a point Q be (p, q)

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 3-3

Given,

The point Q (p, q),

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 3-4

Now,

Let the coordinates of a point E be (⍺, β)

Given,

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 3-5

(iv) Coordinate of the centroid of the ΔABC;

NCERT Exemplar Class 10 Maths Chapter 7 Ex. 7.4 Question 3-6

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