## Chapter 21 Trigonometrical Identities (Including Trigonometrical Ratios of Complementary Angles and Use of Four Figure Trigonometrical Tables) Ex 21D

These Solutions are part of Selina Concise Mathematics Class 10 ICSE Solutions. Here we have given Selina Concise Mathematics Class 10 ICSE Solutions Chapter 21 Trigonometrical Identities Ex 21D.

**Other Exercises**

- Selina Concise Mathematics Class 10 ICSE Solutions Chapter 21 Trigonometrical Identities Ex 21A
- Selina Concise Mathematics Class 10 ICSE Solutions Chapter 21 Trigonometrical Identities Ex 21B
- Selina Concise Mathematics Class 10 ICSE Solutions Chapter 21 Trigonometrical Identities Ex 21C
- Selina Concise Mathematics Class 10 ICSE Solutions Chapter 21 Trigonometrical Identities Ex 21D
- Selina Concise Mathematics Class 10 ICSE Solutions Chapter 21 Trigonometrical Identities Ex 21E

**Question 1.
**

**Use tables to find sine of:**

**(i) 21°**

**(ii) 34°42′**

**(iii) 47° 32′**

**(iv) 62°57′**

**(v) 10°20′ + 20° 45′**

**Solution:**

From tables of sine of angles, we find that:

**(i)**sin 21°= 0.3584,

**(ii)**sin 34°42’= .5693

**(iii)**sin 47° 32′ = 0.7377

**(iv)**sin 62° 57′ = 0.8906

**(v)**sin 10° 20′ + 20°45′ = sin 31°5′

= 0.5162

**Question 2.
**

**Use tables to find cosine of:**

**(i) 2°4′**

**(ii) 8°12′**

**(iii) 26°32’**

**(iv) 65°41′**

**(v) 9°23′ +15°54′**

**Solution:**

From tables of cosine of angle, we find that:

**(i)**cos 2°4′ = 0.9993

**(ii)**cos 8° 12’ = 0.9898

**(iii)**cos 26°32′ = 0.8946

**(iv)**cos 65°41′ = 0.4118

**(v)**cos 9°23′ + 15°54′ = cos 25° 17′

= 0.9042

**Question 3.
**

**Use trigonometrical tables to find tangent of:**

**(i) 37°**

**(ii) 42°18′**

**(iii) 17°27′**

**Solution:**

From the tables of tangents, we find that

**(i)**tan 35° = 0.7536

**(ii)**tan 42°18’= 0.9099

**(iii)**tan 17°27’= 0.3144

**Question 4.
**

**Use tables to find the acute angle θ, if the value of sin θ**

**(i) 4848**

**(ii) 0.3827**

**(iii) 0.6525**

**Solution:**

From the tables of series, we find that of :

(i) sinθ = 0.4848, then θ = 29°

(ii) sinθ = 0.3827, then θ = 20° 30′

(iii) sin θ = 0.6525, then θ = 40° 42’ + 2′ = 40°44′

**Question 5.
**

**Use tables to find the acute angle θ, if the value of cos θ is :**

**(i) 0.9848**

**(ii) 0.9574**

**(iii) 0.6885**

**Solution:**

From the tables of cosines, we find that if :

**(i)**cos θ = 0.9848, then θ = 10°

**(ii)**cos θ = 0.9574, then θ = 16°48′- 1’=16°47’

**(iii)**cos θ = 0.6885, then θ = 46° 30′ or 46°30′

= 46° 29’

**Question 6.
**

**Use tables to find the acute angle θ, if the value of tan θ is :**

**(i) 2419**

**(ii) 0.4741**

**(iii) 0.7391**

**(iv) 1.06**

**Solution:**

From the table of tangents, we find that if:

**(i)**tan θ = 0.2419, then θ=13° 36’

**(ii)**tan θ = 0.4741, then θ = 25° 18’ + 4’ = 25°22′

**(iii)**tan θ = 0.7391, then θ= 36°24’+ 4′ = 36°28′

**(iv)**tan θ = 1.06, then θ = 46°36′ + 4′ = 46°40′

**Question 7.
**

**If sin θ=0.857; find:**

**(i) θ**

**(ii) tan θ**

**Solution:**

From the tables of T. Ratio’s we find this :

**(i)**If sin θ = 0.857, then θ = 58°54′ + 4.5′ = 58° 58′ or 58°59’

**(ii)**tan 58°58’= 1.6577 +43 = 1.662 or tan 58° 59′ = 1.6577 + 53 = 1.663

**Question 8.
**

**If θ is the acute angle and cos θ = 0.7258; find:**

**(i) θ**

**(ii) 2 tan θ – sin θ**

**Solution:**

From the tables of T-ratio’s, we find that:

**(i)**If cos θ = 0.7258, then θ= 43° 30′ -2′ = 43°28’

**(ii)**Now 2 tan θ – sin θ= 2 tan 43°28′ – sin 43°28′

2 tan 43°28’ = 2 x (0.9457 + 0.0022)

= 0:9479 x 2 = 1.8958

and sin 43°28′ = 0.6871 + 0.0008 = 0.6879

∴ 2 tan 43°28′ – sin 43° 28′ = 1.8958 – 0.6879 = 1.2079

**Question 9.
**

**Let θ be an acute angle and tan θ = 0.9490 find:**

(i) θ

(ii) cos θ

(iii) sin θ – cos θ

(i) θ

(ii) cos θ

(iii) sin θ – cos θ

**Solution:**

From the tables of T-raios, we find that:

**(i)**if tan θ = 0.9490 , then θ = 43°30′

**(ii)**cos θ = cos 43°30′ = 0.7254

**(iii)**sin θ = sin 43°50′ = 0.6884

∴ sin θ – cos θ = 0.6884 – 0.7254 = -0.0370 = -0.037

Hope given Selina Concise Mathematics Class 10 ICSE Solutions Chapter 21 Trigonometrical Identities Ex 21D are helpful to complete your math homework.

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