# Math Help - Simple Neg-Angle ID question.

1. ## Simple Neg-Angle ID question.

I know that the Identity is, Cos(-theta) = Cos theta. So, if Cos Theta = -.65, then Cos (-theta) = -.65.......My original answer was Cos (-theta) = .65.......Not sure why it is -.65. Could someone steer me in the right direction here. Thanks

2. Originally Posted by Brndo4u
I know that the Identity is, Cos(-theta) = Cos theta. So, if Cos Theta = -.65, then Cos (-theta) = -.65.......My original answer was Cos (-theta) = .65.......Not sure why it is -.65. Could someone steer me in the right direction here. Thanks
$\cos(\theta) = \cos(-\theta)$ because the cosine function is even.