Science:Math Exam Resources/Courses/MATH200/December 2013/Question 01 (e)/Statement

Suppose it is known that the direction of the fastest increase of the function $f(x,y)$ at the origin is given by the vector $⟨1,2⟩$. Find a unit vector $\text{u}$ that is tangent to the level curve of $f(x,y)$ that passes through the origin.