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-cos(50)/cos(130) - how do I work this out without a calculator?

  • -cos(50)/cos(130) - how do I work this out without a calculator? What is the identity/are the identities I need to use to do this, and how do I do it? Answer should = 1 I think. Thank you!

  • Answer:

    The only identity you need is: cos(180 - x) = -cos x So, -cos(50) / cos(130) = -cos(50) / cos(180 - 50) = -cos(50) / -cos(50) = 1

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Other answers

cos(180-x) = - cos(x) is the identity you need here. This gives: -cos(50) / (-cos(50)) = 1

robby

Best to get familiar with the cosine graph, then you'll understand why cos x = - cos(180-x) So cos150 equals - cos 30 and the answer is clear.

spiffin456

-Cos[50]/Cos[130] = 1

JOS J

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