### Home > CALC > Chapter Ch7 > Lesson 7.4.4 > Problem 7-209

7-209.

Consider the function

*f*(*x*)*= x*^{4/3}− 4*x*^{1/3}. Homework Help ✎Algebraically determine where

*f*is increasing.Algebraically determine whether

*f*is concave up or concave down at*x =*−1.Determine the

*x*-coordinates of all points of inflection.

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.