Let $z \in D$. Show that the function $\Phi : t \mapsto L ( t z )$ is differentiable on an open interval including $[ - 1,1 ]$ and give a simple expression for its derivative on $[ - 1,1 ]$.
Let $z \in D$. Show that the function $\Phi : t \mapsto L ( t z )$ is differentiable on an open interval including $[ - 1,1 ]$ and give a simple expression for its derivative on $[ - 1,1 ]$.