1. Simple Question about Crictical Numbers

Consider the funciton: $f(t)=\mid 3t-4 \mid$,

This function is not differentiable where $f'(t)$ does not exist. This would be at $3t-4=0$. By this reasoning, $\frac{4}{3}$ is a critical number correct?

Consider the funciton: $f(t)=\mid 3t-4 \mid$,
This function is not differentiable where $f'(t)$ does not exist. This would be at $3t-4=0$. By this reasoning, $\frac{4}{3}$ is a critical number correct?