设$f(x)=\begin{cases}a + x^{2},&x\leq0\\\dfrac{1}{x}\sin\dfrac{1}{x},&x > 0\end{cases}$在$x = 0$处连续，求$a$的值.

求不定积分$\int x^{2}\cos xdx$.

求定积分$\int_{0}^{1}\dfrac{x}{\sqrt{1 + x^{2}}}dx$.