Question
Download Solution PDFFind the value of cos 4x
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
cos 2x = cos2 x – sin2 x = 2 cos2 x - 1 = 1 – 2 sin2 x
Calculation:
cos 4x
= cos 2(2x)
= 2 cos2 2x – 1 (∵cos 2x = 2 cos2 x – 1)
= 2 (1 – 2 sin2 x)2 – 1 (∵ cos 2x = 1 – 2 sin2 x)
= 2 [1 – 4 sin2 x + 4 sin4 x] – 1 [∵ (a – b)2 = a2 – 2ab + b2]
= 2 - 8 sin2 x + 8 sin4 x – 1
= 1 - 8 sin2 x + 8 sin4 x
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