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Question
Evaluate:
`(cos75^@)/(sin15^@) + (sin12^@)/(cos78^@) - (cos18^@)/(sin72^@)`
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Solution
`(cos75^@)/(sin15^@) + (sin12^@)/(cos78^@) - (cos18^@)/(sin72^@)`
= `(cos(90^@ - 15^@))/(sin15^@) + (sin(90^@ - 78^@))/(cos78^@) - (cos(90^@ - 72^@))/(sin72^@)`
= `(sin15^@)/(sin15^@) + (cos78^@)/(cos78^@) - (sin72^@)/(sin72^@)`
= 1 + 1 – 1
= 1
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