1. The problem statement, all variables and given/known data 1. Determine the largest open interval where the function f(x)=2x-5/x+3 is increasing AND concave up (at the same time) 2. Relevant equations 3. The attempt at a solution I've run through the problem and arrived at a second derivative of f''(x)= -22/(x+3)^3. Setting this to zero I'm coming back with -3. However, I keep coming back with a situation in which this is concave down. Am I making some sort of error here?