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Complete the left-hand column of the table below following the steps indicated in the right-hand column to show that "sin a sin b = 1/2[cos(a-b)-cos(a+b)]" is an identity. Use the definitions of sum and difference formulas for cosine.

Complete the lefthand column of the table below following the steps indicated in the righthand column to show that sin a sin b 12cosabcosab is an identity Use t class=

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The equations which completes the left-hand column of the table are;

[tex] \frac{1}{2} \cdot \left(cos(a - b) - cos(a + b) \right)[/tex]

  • cos(a - b) - cos(a + b) = (cos(a)•cos(b) + sin(a)•sin(b)) - (cos(a)•cos(b) - sin(a)•sin(b))

  • sin(a)•sin(b) = (1/2)•(cos(a - b) - cos(a + b))

Which equations and identities complete the left-hand column of the table?

The given expression on the right is written as follows;

First row;

[tex] \frac{1}{2} \cdot \left(cos(a - b) - cos(a + b) \right)[/tex]

The definition of the sum and difference of cosine are;

cos(a - b) = cos(a)•cos(b) + sin(a)•sin(b)

cos(a + b) = cos(a)•cos(b) - sin(a)•sin(b)

Therefore;

Second row;

  • cos(a - b) - cos(a + b) = (cos(a)•cos(b) + sin(a)•sin(b)) - (cos(a)•cos(b) - sin(a)•sin(b))

cos(a - b) - cos(a + b) = 2•sin(a)•sin(b)

Which gives;

[tex] sin(a) \cdot sin(b) = \frac{1}{2} \cdot \left(cos(a - b) - cos(a + b) \right)[/tex]

Third row;

  • sin(a)•sin(b) = (1/2)•(cos(a - b) - cos(a + b))

Learn more about trigonometric functions here:

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