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Given cos θ = 0.4, which is the value of cos (θ + π)?

 

The answer is -0.4, how should I get this answer? I have no idea how I should even approach it...

 May 4, 2020
 #1
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In general: cos(a+b) = cos(a)cos(b) - sin(a)sin(b)

 

So:  cos(θ + π) = cos(θ)cos(π) - sin(θ)sin(π)  =  -cos(θ) - 0    = -0.4   since cos(π) = -1  and  sin(π) = 0

 May 4, 2020

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