Evaluate: (i) (ii) (iii) Cos 48° – sin 42° (iv) Cosec 31° – sec 59°

NCERT - Mathematics

Book: NCERT - Mathematics

Chapter: 8. Introduction to Trigonometry

Subject: Maths - Class 10^th

Q. No. 1 of Exercise 8.3

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1

Evaluate:
(i)

(ii)

(iii) Cos 48° – sin 42°

(iv) Cosec 31° – sec 59°

(i)

= 1

(ii)

(iii) cos 48^o - sin 42^o

= cos (90^o - 42^o) – sin 42^o

= sin 42^o - sin 42^o

= 0

(iv) cosec 31^o - sec 59^o

= cosec(90^o - 59^o) – sec 59^o

= sec 59^o - sec 59^o

= 0

1

Chapter Exercises

Exercise 8.1

Exercise 8.2

Exercise 8.3

Exercise 8.4

Testing

1

Evaluate:
(i)

(ii)

(iii) Cos 48° – sin 42°

(iv) Cosec 31° – sec 59°

2

Show that:
(i) tan 48° tan 23° tan 42° tan 67° = 1
(ii) cos 38° Cos 52° – sin 38° sin 52° = 0

3

If tan 2A = cot (A – 18°), where 2A is an acute angle, find the value of A

4

If tan A = cot B, prove that A + B = 90°

5

If sec 4A = cosec (A – 20°), where 4A is an acute angle, find the value of A

6

If A, B and C are interior angles of a triangle ABC, then show that

7

Express sin 67° + Cos 75° in terms of trigonometric ratios of angles between 0° and 45°