For this part we know that \(7 > - 4\) and so there will be values of \(z\) on both sides of 7 in the range \(z > - 4\) and so we can assume that, in the limit, we will have \(z > - 4\). This will allow us to use the piece of the function in that range and then just use standard limit techniques to compute the limit.

\[\mathop {\lim }\limits_{z \to 7} h\left( z \right) = \mathop {\lim }\limits_{z \to 7} \left( {1 - 9z} \right) = \require{bbox} \bbox[2pt,border:1px solid black]{{ - 62}}\]

This part is going to be different from the previous part. We are looking at the limit at \(z = - 4\) and that is the “cut–off” point in the piecewise functions. Recall from the discussion in the section, that this means that we are going to have to look at the two one sided limits.

\[\mathop {\lim }\limits_{z \to \, - {4^{\, - }}} h\left( z \right) = \mathop {\lim }\limits_{z \to \, - {4^{\, - }}} 6z = \underline { - 24} \hspace{0.25in}\hspace{0.25in}{\mbox{because }}z \to - {4^ - }{\mbox{ implies that }}z < - 4\] \[\mathop {\lim }\limits_{z \to \, - {4^{\, + }}} h\left( z \right) = \mathop {\lim }\limits_{z \to \, - {4^{\, + }}} \left( {1 - 9z} \right) = \underline {37} \hspace{0.25in}{\mbox{because }}z \to - {4^ + }{\mbox{ implies that }}z > - 4\]

So, in this case, we can see that,

\[\mathop {\lim }\limits_{z \to \, - {4^{\, - }}} h\left( z \right) = - 24 \ne 37 = \mathop {\lim }\limits_{z \to \, - {4^{\, + }}} h\left( z \right)\]

and so we know that the overall limit does not exist.