. Find (on the paper) the extrema of f : (x1, x2, x3) 7 f(x1, x2, x3) = x 2 1 + (x1 +x2) 2 + (x1 +x3) 2 . Justify your answers. Use an optimizer in R, Matlab or Python to verify your answer.. 2. Is the function defined by function f : (x1, x2, x3) 7 f(x1, x2, x3) = x 4 1 + (x1 + x2) 2 + (x1 + x3) 2 convex or concave over R 3 ?. Write a computer program in R, Matlab or Python to verify your answer.