What about the Hessian matris in looking for the convexity.
As far as i know, If the Hessian matrice is positive definite: the function is strictly convex, If it is positive semidefinite it is convex. And if the Hessian is negative than concave. Am i right?
Originally Posted by Last_Singularity
Convexity is determined by the sign of the second order derivative.
Linear and quadratic approximations can be obtained by finding the Taylor Series expansion of the function
Please try out the problem first and let us know where you get stuck.