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If a cosalpha+bsin alpha=c=a cos beta+b ...

If a `cosalpha+bsin alpha=c=a cos beta+b sin beta` then prove that
`frac{a}{cosfrac{1}{2}(alpha+beta)` = ` frac{b}{sinfrac{1}{2}(alpha+beta)` =` frac {c}{cosfrac{1}{2}(alpha-beta)`

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MBD PUBLICATION-TRIGONOMETRIC FUNCTIONS-QUESTION BANK
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