In: Advanced Math
Let f(x,y) = 3x3 + 3x2 y − y3 − 15x.
a) Find and classify the critical points of f. Use any method taught during the course (the second-derivative test or completing the square).
b) One of the critical points is (a,b) = (1,1). Write down the second-degree Taylor approximation of f about this point and motivate, both with computations and with words, how one can see from this approximation what kind of critical point (1,1) is. Use completing the square.