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Question
Evaluate: cos2 25° - sin2 65° - tan2 45°
Sum
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Solution
cos2 25° - sin2 65° - tan2 45°
= [cos(90° - 65°)]2 - sin2 65° - (tan 45°)2
= sin2 65° - sin2 65° - (1)2
= 0 - 1
= - 1.
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