emiliefowkes emiliefowkes
  • 26-05-2020
  • Mathematics
contestada

If im given cos81 = 0.1564, how do i evaluate other cosines without a calculator? Like cos99 and cos279 for example.

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ronhagrid310
ronhagrid310 ronhagrid310
  • 26-05-2020

Answer:

As property of trigonometry:

cos x = - cos(180 - x)

=> cos 99 = - cos(180 - 99) = - cos 81 = - 0.1564

cos x = cos(360 - x)

=> cos 279 = cos(360 - 279) = cos 81 = 0.1564

Hope this helps!

:)

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