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Question
Find the value of the following:
cos 70° cos 10° – sin 70° sin 10°
Sum
Solution
Given that cos 70° cos 10° – sin 70° sin 10°
(This is of the form of cos (A + B), A = 70°, B = 10°)
= cos (70° + 10°)
= cos 80°
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Trigonometric Ratios of Compound Angles
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Chapter 4: Trigonometry - Exercise 4.2 [Page 84]
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