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Expression : $$2cos^2A - 1 = x$$
$$\because$$ $$(sin^2A+cos^2A=1)$$
= $$2cos^2A-(sin^2A+cos^2A)$$
= $$2cos^2A-cos^2A-sin^2A$$
= $$cos^2A-sin^2A = (cos^2A-sin^2A) \times (1)$$
= $$(cos^2A-sin^2A) \times (cos^2A+sin^2A)$$
= $$cos^4A-sin^4A$$
=> Ans - (B)
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