NCERT Solutions
Class 10 - Mathematics - Chapter 8: INTRODUCTION TO TRIGONOMETRY
Exercise 8.1

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Question. 1

In ΔABC, right-angled at B, AB = 24 cm, BC = 7 cm. Determine:

(i) sin A, cos A

(ii) sin C, cos C

Answer:

(i) sin A = \(\frac{7}{25}\), cos A = \(\frac{24}{25}\)

(ii) sin C = \(\frac{24}{25}\), cos C = \(\frac{7}{25}\)

Question. 2

In Fig. 8.13, find tan P − cot R.

Answer:

0

Question. 3

If sin A = \(\frac{3}{4}\), calculate cos A and tan A.

Answer:

cos A = \(\frac{\sqrt{7}}{4}\), tan A = \(\frac{3}{\sqrt{7}}\)

Question. 4

Given 15 cot A = 8, find sin A and sec A.

Answer:

sin A = \(\frac{15}{17}\), sec A = \(\frac{17}{8}\)

Question. 5

Given sec θ = \(\frac{13}{12}\), calculate all other trigonometric ratios.

Answer:

sin θ = \(\frac{5}{13}\), cos θ = \(\frac{12}{13}\), tan θ = \(\frac{5}{12}\), cot θ = \(\frac{12}{5}\), cosec θ = \(\frac{13}{5}\)

Question. 6

If ∠A and ∠B are acute angles such that cos A = cos B, then show that ∠A = ∠B.

Question. 7

If cot θ = \(\frac{7}{8}\), evaluate:

(i) \(\frac{(1 + \sin θ)(1 - \sin θ)}{(1 + \cos θ)(1 - \cos θ)}\)

(ii) cot² θ

Answer:

(i) \(\frac{49}{64}\)

(ii) \(\frac{49}{64}\)

Question. 8

If 3 cot A = 4, check whether \(\frac{1 - \tan^2 A}{1 + \tan^2 A} = \cos^2 A - \sin^2 A\) or not.

Answer:

Yes

Question. 9

In triangle ABC, right-angled at B, if tan A = \(\frac{1}{\sqrt{3}}\), find:

(i) sin A cos C + cos A sin C

(ii) cos A cos C − sin A sin C

Answer:

(i) 1

(ii) 0

Question. 10

In ΔPQR, right-angled at Q, PR + QR = 25 cm and PQ = 5 cm. Determine sin P, cos P and tan P.

Answer:

sin P = \(\frac{12}{13}\)

cos P = \(\frac{5}{13}\)

tan P = \(\frac{12}{5}\)

Question. 11

State whether the following are true or false. Justify your answer:

(i) The value of tan A is always less than 1.

(ii) sec A = \(\frac{12}{5}\) for some value of angle A.

(iii) cos A is the abbreviation used for the cosecant of angle A.

(iv) cot A is the product of cot and A.

(v) sin θ = \(\frac{4}{3}\) for some angle θ.

Answer:

(i) False

(ii) True

(iii) False

(iv) False

(v) False

Disclaimer:The solutions provided here are prepared independently for educational purposes only. This material is not an official NCERT publication.
NCERT Solutions Class 10 – Mathematics – Chapter 8: INTRODUCTION TO TRIGONOMETRY – Exercise 8.1 | Detailed Answers