342

a)
$f\left(x\right)=3x^2$

$f'\left(1\right)=\lim_{x\rightarrow1}\ \frac{3x^2-3}{x-1}=\frac{3\left(x-1\right)\left(x+1\right)}{x-1}=3x+3=6$
$f'\left(a\right)=\lim_{x\rightarrow a}\ \frac{3x^2-3a}{x-a}=\frac{3\left(x-a\right)\left(x+a\right)}{x-a}=3x+3a=6a$

b)
$f'\left(x\right)=6x$
c)
$f'\left(-2\right)=6\left(-2\right)=-12$