Question
Evaluate the following limit:
$\lim\limits_{\text{h}\rightarrow0}\frac{\text{(a}+\text{h})^2\sin(\text{a}+\text{h})-\text{a}^2\sin\text{a}}{\text{h}}$

Answer

$\lim\limits_{\text{h}\rightarrow0}\frac{\text{(a}+\text{h})^2\sin(\text{a}+\text{h})-\text{a}^2\sin\text{a}}{\text{h}}$
$=\lim\limits_{\text{h}\rightarrow0}\frac{\big(\text{a}^2+\text{h}^2+2\text{ah}\big)\sin(\text{a}+\text{h})-\text{a}^2\sin\text{a}}{\text{h}}$
$=\lim\limits_{\text{h}\rightarrow0}\frac{\text{a}^2\sin(\text{a}+\text{h})+\text{h}^2\sin(\text{a}+\text{h})+2\text{ah}\sin(\text{a}+\text{h})-\text{a}^2\sin\text{a}}{\text{h}}$
$=\lim\limits_{\text{h}\rightarrow0}\Big[\frac{\text{a}^2(\sin(\text{a}+\text{h})-\sin\text{a})}{\text{h}}+\frac{\text{h}^2\sin(\text{a}+\text{h})}{\text{h}(\text{a}+\text{h})}\times(\text{a}+\text{h})+\frac{2\text{ah}}{\text{h}}(\sin(\text{a}+\text{h}))\Big]$
$=\Bigg[\text{a}^2\lim\limits_{\text{h}\rightarrow0}\frac{2\cos\big(\frac{\text{a}+\text{h}+\text{a}}{2}\big)\sin\big(\frac{\text{a}+\text{h}-\text{a}}{2}\big)}{\text{h}}\Bigg]+[0]+2\text{a}\lim\limits_{\text{h}\rightarrow0}\sin(\text{a}+\text{h})$
$=\Big(2\text{a}^2\cos\text{a}\times\frac12\Big)+(2\text{a}\sin\text{a})$
$=\text{a}^2\cos\text{a}+2\text{a}\sin\text{a}$

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