# Gujarat Board Solutions Class 10 Maths Chapter 8 Introduction to Trigonometry Ex 8.4

Gujarat Board Solutions Class 10 Maths Chapter 8 Introduction to Trigonometry Ex 8.4

## Gujarat Board Textbook Solutions Class 10 Maths Chapter 8 Introduction to Trigonometry Ex 8.4

Question 1.

Express the trigonometric ratios sin A, sec A and tan A in terms of cot A. (CBSE 2012)

Solution:

(ii) sin 25° cog 65° + cos 25° sin 65°

= sin 25° cos (90° – 25°) + cos 25° sin (90° – 25°)

= sin 25° sin 25° + cos 25° cos 25°

= sin^{2} 25° + cos^{2} 25

= 1

Question 4.

Choose the correct option. Justify your choice.

(i) 9 sec^{2} θ – 9 tan^{2} θ =

(a) 1

(b) 9

(c) 8

(d) 0

(ii) (1 + tan θ + sec θ) (1 + cot θ – cosec θ)=

(a) –

(b) 1

(c) 2

(d) -1

(iii) (sec A + tan A) (1 – sin A) =

(a) sec A

(b) sin A

(c) cosec A

(d) cos A

Question 5.

Prove that the following identities, where the angles involved are acute angles for which the expression are defined.

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