Given vertices $A(1,\,1),B(4,\, - 2)$ and $C(5,\,5)$ of a triangle, then the equation of the perpendicular dropped from $C$ to the interior bisector of the angle $A$ is
→If $f(x) = \left\{ \begin{array}{l}\sin x,x \ne n\pi ,n \in Z\\\,\,\,\,\,\,0,\,\,{\rm{otherwise}}\end{array} \right.$ and $g(x) = \left\{ \begin{array}{l}{x^2} + 1,x \ne 0,\,2\\\,\,\,\,\,\,\,\,4,x = 0\\\,\,\,\,\,\,\,\,\,5,x = 2\end{array} \right.$ then $\mathop {\lim }\limits_{x \to 0} g\{ f(x)\} = $
→Let $a_1, a_2, a_3, \ldots, a_{100}$ be an arithmetic progression with $a_1=3$ and $S_p=\sum_{i=1}^p a_i, 1 \leq p \leq 100$. For any integer $n$ with $1 \leq n \leq 20$, let $m=5 n$. If $\frac{S_{m m}}{S_n}$ does not depend on $n$, then $a_2$ is
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