Selina Solutions Class 10 Maths Chapter 21 Trigonometrical Identities
Selina Solutions Concise Maths Class 10 Chapter 21 Trigonometrical Identities Exercise 21(D)
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:
(i) sin 21o = 0.3584
(ii) sin 34o 42’= 0.5693
(iii) sin 47o 32’= sin (47o 30′ + 2′) =0.7373 + 0.0004 = 0.7377
(iv) sin 62o 57′ = sin (62o 54′ + 3′) = 0.8902 + 0.0004 = 0.8906
(v) sin (10o 20′ + 20o 45′) = sin 30o65′ = sin 31o5′ = 0.5150 + 0.0012 = 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:
(i) cos 2° 4’ = 0.9994 – 0.0001 = 0.9993
(ii) cos 8° 12’ = cos 0.9898
(iii) cos 26° 32’ = cos (26° 30’ + 2’) = 0.8949 – 0.0003 = 0.8946
(iv) cos 65° 41’ = cos (65° 36’ + 5’) = 0.4131 -0.0013 = 0.4118
(v) cos (9° 23’ + 15° 54’) = cos 24° 77’ = cos 25° 17’ = cos (25° 12’ + 5’) = 0.9048 – 0.0006 = 0.9042
Question 3. Use trigonometrical tables to find tangent of:
(i) 37°
(ii) 42° 18′
(iii) 17° 27′
Solution:
(i) tan 37o = 0.7536
(ii) tan 42o 18′ = 0.9099
(iii) tan 17o 27′ = tan (17o 24′ + 3′) = 0.3134 + 0.0010 = 0.3144
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