9. Construct an example of a strictly quasiconcave function that is not a concave function. 10. Using the points x’ = 1, x” = 9, and A = 5/8. illustrate definition 2.25 for the concave function y = x'”, x > 0. Use a graph in your answer. 11. Show that the function y = xm, x > 0. is strictly concave according to definition 2.25. 12. Show that the function f(x] , X3) = x12 + x22 is strictly convex according to definition 2.26.