Failure is not an option. Use the product-to-sum identities to rewrite the following expressions as a sum or differe b. \( 2 \cos (2 \beta) \cos (2 \beta) \)
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To rewrite the expression \( 2 \cos (2 \beta) \cos (2 \beta) \) using product-to-sum identities, we can employ the formula \( 2 \cos A \cos B = \cos(A+B) + \cos(A-B) \). Here, since both \( A \) and \( B \) are \( 2 \beta \), we substitute into the formula: \[ 2 \cos(2\beta) \cos(2\beta) = \cos(2\beta + 2\beta) + \cos(2\beta - 2\beta) = \cos(4\beta) + \cos(0) \] Since \( \cos(0) = 1 \), we arrive at the final expression: \[ \cos(4\beta) + 1 \] So, \( 2 \cos (2 \beta) \cos (2 \beta) = \cos(4\beta) + 1 \).