Which derivation correctly uses the cosine sum identity to prove the cosine double angle identity?

Question

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Table with 2 columns and 4 rows.Row 1: Column 1, empty; Column 2, 'Step' Row 2: Column 1, '1.'; Column 2, 'cosine of 2 x is equal to cosine of open paren x plus x close paren' Row 3: Column 1, '2.'; Column 2, 'is equal to cosine x minus sine x' Row 4: Column 1, '3.'; Column 2, 'is equal to cosine squared of x minus sine squared of x'

Trigonometric Double Angle Identities - Quiz Quiz

Which derivation correctly uses the cosine sum identity to prove the cosine double angle identity?

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