Math, asked by Anonymous, 1 year ago

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Answers

Answered by siddhartharao77
5

Step-by-step explanation:

LHS:

cos 4A

= cos(2.2A)

= 2 cos² (2A) - 1

= 2(2 cos² 2A - 1)² - 1

= 2(4 cos⁴ A - 4 cos² A + 1) - 1

= 8 cos⁴ A - 8 cos² A + 1

RHS

Hope it helps!


siddhartharao77: :-)
Anonymous: i didn't understand last 2nd step.. can u elaborate plz?
siddhartharao77: (a - b)^2 = a^2 + b^2 - 2ab. Here a = 2cos2A, = 1
siddhartharao77: Any doubts?
Anonymous: thn it shud be 4cos^2A - 4cos2A +1..
siddhartharao77: Mistake... Let me correct
Anonymous: sure :)
siddhartharao77: Done. Thanks
siddhartharao77: Did u understand the answer?
Anonymous: yes.. tnx
Answered by Siddharta7
1

cos (4A) = cos (2•(2A))

↔ cos (2•(2A)) = 2•cos² (2A) - 1

↔ cos (4A) = 2•cos² (2A) - 1

↔ cos (4A) = 2•(2•cos² A - 1)² - 1

↔ cos (4A) = 2•(2•cos² A - 1)² - 1

↔ cos (4A) = 2•{4•(cos² A)² - 4•(cos² A) + 1} - 1

↔ cos (4A) = 8•cos⁴ A - 8•cos² A + 2 - 1

↔ cos (4A) = 8•cos⁴ A - 8•cos² A + 1

↔ cos (4A) = 1 - 8•cos² A + 8•cos⁴ A .... qid

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