The value of cos^4 A-sin^4 A is
(a) sin 2A
(b)cos 2A
(c) tan 2A
(d) sec 2A
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Answer:
(b) cos2A is the answer
Step-by-step explanation:
cos ^4A-sin^4A
=(cos^2A)^2-(sin^2A)^2. {a^2-b^2=(a+b)(a-b)}
=(cos^2A+sin^2A)(cos^2A-sin^2A)
=1(cos2A)
=cos2A
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