How do you find the unit vector, in the first quadrant, that is parallel to the line tangent to the parabola y = x^2 at the point (4, 16)?
(1/sqrt 65, 8/sqrt 65)
The slope of the tangent
So, the principal value of
For the opposite direction,
be < 0... .
The unit vector for inclination
The unit vector in this direction could be anywhere in the plane.
The reference to first quadrant, for its presence, is not necessary..