Solution
Expression : $$(cos^4 A - sin^4 A)$$
= $$(cos^2A-sin^2A)(cos^2A+sin^2A)$$
$$\because(cos^2A+sin^2A=1)$$
= $$(cos^2A-sin^2A)(1)=cos^2A-sin^2A$$
= $$cos2A$$
=> Ans - (C)
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