My teacher is telling me that the below function is quasiconcave, but I think it is not. 1. The problem statement, all variables and given/known data Show that u(c, l) = 20 000 c + c2+ l is or is not quasiconcave, in the first quadrant. c>=0 and l>=0. 2. Relevant equations From wikipedia: 3. The attempt at a solution I've rewriten it, for some level curve, as l = M + 10000 + (c+100)2, so it looks like a circle. Since the function u is increasing in both arguments, the upper level set looks like the outside of the circle, which is not convex, therefore the function is not quasiconcave. Correct? We are talking here only about the first quadrant.