Relate graph direction and instantaneous rate
The segment through P and Q is the tangent to the smooth curve at the stated input
\[f(x)=-x^{2}-2\]
\[x=-1,\quad P=(-\frac{3}{2},-4),\quad Q=(-\frac{1}{2},-2)\]
The segment through P and Q is the tangent to the smooth curve at the stated input