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NCERT Exemplar · Class 9 · Maths

Chapter 7: Triangles

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

Exercise 7.1

Textbook page 64 · 5 questions
Q1Multiple choice

Which of the following is not a criterion for congruence of triangles?

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Correct option: C
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Worked solution

(C) SSA

Explanation:

We know that,

Two triangles are congruent, if the side(S) and angles (A) of one triangle is equal to another.

And criterion for congruence of triangle are SAS, ASA, SSS, and RHS.

SSA is not the criterion for congruency of a triangle.

Hence, option C is the correct answer.

Q2Written answer

If AB = QR, BC = PR and CA = PQ, then

(A) Δ ABC ≅ ΔPQR

(B) ΔCBA ≅ ΔPRQ

(C) ΔBAC ≅ Δ RPQ

(D) Δ PQR ≅ Δ BCA

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Worked solution

(B) ΔCBA ≅ ΔPRQ

Explanation:

According to the question,

AB = QR, BC = PR and CA = PQ

Since, AB = QR, BC = PR and CA = PQ

We can say that,

A corresponds to Q, B corresponds to R, C corresponds to P.

NCERT Exemplar Solutions For Class 9 Maths Chapter 7 Exercise 7.1-1

Hence, (B) ΔCBA ≅ ΔPRQ

Hence, option B is the correct answer.

Q3Written answer

In Δ ABC, AB = AC and ∠B = 50°. Then ∠C is equal to

(A) 40° (B) 50° (C) 80° (D) 130°

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Worked solution

(B) 50°

Explanation:

According to the question,

Δ ABC, AB = AC and ∠B = 50°.

NCERT Exemplar Solutions For Class 9 Maths Chapter 7 Exercise 7.1-2

Since, AB = AC

Δ ABC is an isosceles triangle.

Hence, ∠B = ∠C

∠B = 50° (given)

⇒ ∠C = 50°

Hence, option B is the correct option.

Q4Written answer

In Δ ABC, BC = AB and ∠B = 80°. Then ∠A is equal to

(A) 80° (B) 40° (C) 50° (D) 100°

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Worked solution

(C) 50°

Explanation:

Given: Δ ABC, BC = AB and ∠B = 80°

NCERT Exemplar Solutions For Class 9 Maths Chapter 7 Exercise 7.1-3

Since, BC = AB

Δ ABC is an isosceles triangle.

Let, ∠C = ∠A = x

∠B = 80° (given)

We know that,

Using angle sum property,

Sum of interior angles of a triangle should be = 180o

∠A + ∠B + ∠C = 180°

⇒ x + 80° + x = 180°

⇒ 2x = 180° – 80°

⇒ 2x = 100°

⇒ x = 50°

Therefore, ∠C = ∠A = 50°

Hence, option C is the correct answer.

Q5Written answer

In Δ PQR, ∠R = ∠P and QR = 4 cm and PR = 5 cm. Then the length of PQ is

(A) 4 cm (B) 5 cm (C) 2 cm (D) 2.5 cm

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Worked solution

Given: ΔPQR, ∠R = ∠P and QR = 4 cm and PR = 5 cm

NCERT Exemplar Solutions For Class 9 Maths Chapter 7 Exercise 7.1-4

Since, ∠R = ∠P

Δ PQR is an isosceles triangle.

Hence, PQ = QR

⇒ PQ = 4cm

Hence, option A is the correct answer.