Question: Find the following limits

(a) \(\underset{x\to 1}{\mathop{\lim }}\,\left( {{x}^{2}}-1 \right)\left( {{x}^{2}}+x+1 \right)\)

(b) \(\underset{x\to 2}{\mathop{\lim }}\,\frac{{{x}^{3}}+2x}{x-1}\)

(c) \(\underset{x\to 1}{\mathop{\lim }}\,\frac{{{x}^{2}}+x+1}{x-1}\)