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Question
Find the values of the following trigonometric ratio.
cos (-210°)
Sum
Solution
cos(-210°) = cos 210° (∵ cos(-θ) = cos θ)
[∵ 180 + 30°. No change in T-ratio. 210° lies 3rd quadrant ‘cos’ is negative]
= cos(180° + 30°)
= - cos 30°
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Trigonometric Ratios
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Chapter 4: Trigonometry - Exercise 4.1 [Page 81]
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