The directions say to find the points of inflection and discuss the concavity of the graph of the function.

The function is

$\displaystyle f(x)= sinx+cosx$ the intervals [0,2$\displaystyle pi$]

I know you supposed to take the derivative, then the 2nd then set the equation to zero

so i have up to

$\displaystyle 0= cosx-sinx$

Is this right?

if so what do i do next?