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Grade 8IIT JEE Entrance Exam

Arun the answer u gave may be the correct but it was not appropriate for my options I have sent the questions and as well as options . the question no is 3 can I get answer as quickly as possible please

Question image for Arun the answer u gave may be the correct but it
Profile image of Harshitha
7 Years agoGrade 8
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1 Answer

Profile image of Arun
7 Years ago
Cos3a = 4cosa - 3cos³a, sin3a = 3sina - 4sin³a,
substituting we get, 
(4cos³a - 3cosa - 3sina + 4sin³a)/cosa+sina 
= 4(cos³a + sin³a) - 3(cosa+sina) / cosa+ sina
= 4(cos²a+sin²a-sinacosa) - 3
= 4 - 3 - 4sinacosa 
= 1 - 2sin2a. 
 
hence option 2 is correct

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