# Introduction to Trigonometry – Exercise 8.4 – Class 10

1. Express the trigonometric ratios sin A, sec A and tan A in terms of cot A.

Solution:

We know that,

2. Write all the other trigonometric ratios of ∠A in terms of sec A.

Solution:

We know that

3. Evaluate (i) (sin263° + sin227°)/(cos217°+cos273°)

(ii) sin25° cos65° + cos25° sin65°

Solution:

(i)

(ii)sin25° cos65° + cos25° sin65°

= (sin25°){cos(90°-25°)} + cos25°{sin(90°-25°)}

= (sin25°)(sin25°)+(cos25°)(cos25°)

= (sin225°) + cos225°

= 1

4. Choose the correct option. Justify your choice.

(i) 9 sec2A − 9 tan2 A =

(A) 1

(B) 9

(C) 8

(D) 0

(ii) (1 + tan θ + sec θ) (1 + cot θ − cosec θ)

(A) 0

(B)1

(C) 2

(D) −1

(iii) (secA + tanA) (1 − sinA) =

(A) secA

(B) sinA

(C) cosecA

(D) cosA

(iv)(1+tan2A)/(1+cot2A) =

(A) sec2A

(B) -1

(d) tan2A

Solution:

(i) 9 sec2 A − 9 tan2 A

= 9 (sec2 A – tan2 A)

= 9 (1)  [Because  sec2 A − tan2 A = 1]

= 9

(B) is correct.

(ii) (1 + tan θ + sec θ) (1 + cot θ − cosec θ)

(C) is correct.

(iii)

= cosA

(D) is correct.

(iv)

(D) is correct.

5. Prove the following identities, where the angles involved are acute angles for which the expressions are defined.

Solution:

Solution:

(iii)

Solution:

= secθ cosec θ + 1 = R.H.S.

(iv)

Solution:

(v)

solution:

= cosec A + cot A = R.H.S

(vi)

Solution:

## 9 thoughts on “Introduction to Trigonometry – Exercise 8.4 – Class 10”

1. Very nice post! I have seen first in WordPress. Can you please tell me how you write mathematical numbers in your blog because its difficult to show powers or exponents what app you used. Can you please tell me.

1. Yeah sure… we have many mathematical symbol in WordPress itself . Very few like fractions that we need to do write in HTML page and other symbols like cube root, 4th root, nth root etc are easy to write in word document ,then we need to copy it to WordPress