You need to evaluate the expression using the formula `cos a*cos b - sin a*sin b = cos (a + b)` . You need to put `a = pi/7` and `b = pi/5,` such that:
`cos (pi/7)*cos ((pi)/5) - sin (pi/7) *sin (pi/5) = cos (pi/7 + pi/5)`
`cos (pi/7)*cos ((pi)/5) - sin (pi/7) *sin (pi/5) = cos ((12pi)/35)`
Hence, evaluating the given expression yields that it is the cosine of the sum of the...
You need to evaluate the expression using the formula `cos a*cos b - sin a*sin b = cos (a + b)` . You need to put `a = pi/7` and `b = pi/5,` such that:
`cos (pi/7)*cos ((pi)/5) - sin (pi/7) *sin (pi/5) = cos (pi/7 + pi/5)`
`cos (pi/7)*cos ((pi)/5) - sin (pi/7) *sin (pi/5) = cos ((12pi)/35)`
Hence, evaluating the given expression yields that it is the cosine of the sum of the angles `a = pi/7` and `b = pi/5` , such that `cos (pi/7)*cos ((pi)/5) - sin (pi/7) *sin (pi/5) = cos ((12pi)/35).`
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