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...
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
