# 316: Differentiation - Increasing and decreasing - An increasing function

The function $f\left( x \right) = {x^3} + x$ is always increasing. You can see that its gradient is never negative.

The function $f\left( x \right) = {x^3}$ has a gradient of zero at $x = 0$. This is also an increasing function, but is it

The function $f\left( x \right) = {x^3}$ has a gradient of zero at $x = 0$. This is also an increasing function, but is it

**increasing?***strictly*