Question: Evaluate the following limits if they exist. If a limit does not exist, explain why.

a) \[\underset{a\to 1}{\mathop{\lim }}\,\frac{{{a}^{2}}+6a-7}{a-1}\]

b) \[\underset{x\to 0}{\mathop{\lim }}\,\frac{\cos x}{x}\]

c) \[\underset{x\to {{0}^{+}}}{\mathop{\lim }}\,\ln x\]