$A=\underset{h\to 0}{\mathop{\lim }}\,(\frac{f(3+2h)-f(3-h)}{h})\times \frac{{{f}^{2}}(3+2h)+f(3+2h)f(3-h)+{{f}^{2}}(3-h)}{h-1}$

$=\underset{h\to 0}{\mathop{\lim }}\,(\frac{f(3+2h)-f(3-h)}{h})\times (\frac{{{f}^{2}}(3)+{{f}^{2}}(3)+{{f}^{2}}(3)}{-1})$

$=\left[ 2\underset{h\to 0}{\mathop{\lim }}\,\frac{f(3+2h)-f(3)}{2h}+\underset{h\to 0}{\mathop{\lim }}\,\frac{f(3-h)-f(3)}{-h} \right]\times (-3{{f}^{2}}(3))=3{f}'(3).(-3{{f}^{2}}(3))$

$\Rightarrow f(3)={{(3)}^{2}}-2(3)=3$ 

برای $x$‌های مثبت $\Rightarrow {f}'(x)=2x-2$ 

$\Rightarrow {f}'(3)=2(3)-2=4$ 

$3{f}'(3).(-3.{{f}^{2}}(3))=3(4).(-3{{(3)}^{2}})=-324$