Question #26248

1 Answer
Jan 28, 2018

#-0.9#

Explanation:

Rotating an angle by #pi# flips it 180 degrees around the circle.

This means that both its #x# and #y# coordinates are flipped (made negative).

Since #cos# is just the #x# coordinate of an angle on the unit circle, and rotating that angle by #pi# will flip its #x# coordinate (and its #y# too, but that's not important right now) we can say that:

#cos(theta+pi) = -costheta#

Therefore:

#if costheta = 0.9#

#"then" cos(theta+pi) = -0.9#

Final Answer