cos 52° + cos 68° + cos 172° का मान है।(A) 0 (B) 1

1.	cos 52° + cos 68° + cos 172° का मान है।(A) 0 (B) 1 \| (C)-1 (D) -(A) (B) ) (D) } (C)5. 18 जनवरी, 2018 को जीएसटी परिषद की 25वीं बैठक कहां सम्पन्नहुआ?(A) मणिपुर(B) जम्मू-कश्मीर(C) बंगलुरू(D) नई दिल्ली(B) ।() (A) \| () (C)Y ALP/TECH. STAGE-1, TEST SERIES, VOL.-1.RT 27
Answer» 4)-1 and 5)B this is the answer of your questions Answer:A)0Explanation:First of all cos 172 = -cos 8So now we have= cos 52 + cos 68 - cos 8 Applying Identity,cos A − cos B = −2 sin ½ (A + B) sin ½ (A − B) Now, cos 52 - cos8, here let's A = 52, B=8cos 52 - cos 8 = -2sin[60/2]sin[44/2]cos52 -cos8 = - sin 22socos 52 + cos 68 + cos172= cos52 + cos68 - cos8= cos52 - cos8 + cos68= - sin22 + cos68but by the complementary relationshipsin 22 = cos68 , (since 22+68 = 90)so finally= -cos 68 + cos 68= 0 newdelhi is right ans D

cos 52° + cos 68° + cos 172° का मान है।(A) 0 (B) 1 | (C)-1 (D) -(A) (B) ) (D) } (C)5. 18 जनवरी, 2018 को जीएसटी परिषद की 25वीं बैठक कहां सम्पन्नहुआ?(A) मणिपुर(B) जम्मू-कश्मीर(C) बंगलुरू(D) नई दिल्ली(B) ।() (A) | () (C)Y ALP/TECH. STAGE-1, TEST SERIES, VOL.-1.RT 27

Answer»

4)-1 and 5)B this is the answer of your questions

Answer:A)0Explanation:First of all cos 172 = -cos 8So now we have= cos 52 + cos 68 - cos 8

Applying Identity,cos A − cos B = −2 sin ½ (A + B) sin ½ (A − B)

Now, cos 52 - cos8, here let's A = 52, B=8cos 52 - cos 8 = -2sin[60/2]sin[44/2]cos52 -cos8 = - sin 22socos 52 + cos 68 + cos172= cos52 + cos68 - cos8= cos52 - cos8 + cos68= - sin22 + cos68but by the complementary relationshipsin 22 = cos68 , (since 22+68 = 90)so finally= -cos 68 + cos 68= 0

newdelhi is right ans D

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