is the angle between a horizontal ray directed to the right (say, the positive x-axis) and a nonhorizontal, nonvertical line L, show that the slope m of L equals
tangent thetatanθ,
then the angle
thetaθ
is called the inclination of L. [Hint: See the illustration, where line M has been drawn parallel to L and passing through the origin. Use the fact that M intersects the unit circle at the point
(cosine theta,sine thetacosθ,sinθ).]