1. ## Concavity

17. For what value of x is the graph of y = 2 / (4 - x) concave downwards?

I found the first derivative = 2/(4-x)^2

And then the second 4/(4-x)^3

But I think I might have messed up somewhere in there

2. Originally Posted by karisrou
17. For what value of x is the graph of y = 2 / (4 - x) concave downwards?

I found the first derivative = 2/(4-x)^2

And then the second 4/(4-x)^3

But I think I might have messed up somewhere in there
Concave down for values of x satisfying f''(x) < 0. In your case this happens for x > 4. (This is evident from the graph).