### Home > CALC > Chapter 7 > Lesson 7.4.4 > Problem 7-209

7-209.

Where is *f* '(*x*) positive?

Solve *f* ''(*x*) > 0 and *f* ''(*x*) < 0.

An inflection point occurs where *f* ''(*x*) undergoes a sign change.

Sometimes that happens where *f* ''(*x*) = 0 and sometimes where *f* ''(*x*) = DNE.