ans
18237
A


18238
D


18239
B


18240
C


18241
D


18242
D


18243
B


18244
C


18245
C


18246
B


18247
$1$


18248
$\dfrac{x^2}{2}-\dfrac{y^2}{2}=1$


18249
$\dfrac{9\pi}{4}$, $\dfrac{\pi}{3}$


18250
$48$, $384$


18251
\textcircled{2}\textcircled{3}


18252
(1) 证明略; (2) $\dfrac{\pi}{3}$


18253
(1) $\varphi=-\dfrac{\pi}{3}$; (2) 选条件\textcircled{1}不能使函数$f(x)$存在, 条件\textcircled{2}\textcircled{3}均可解得$\omega = 1$, $\varphi=-\dfrac{\pi}{6}$


18254
(1) $0.4$; (2) $0.168$; (3) 不变的概率最大


18255
(1) $\dfrac{x^2}{9}+\dfrac{y^2}{4}=1$; (2) 证明略


18256
(1) $a=-1$, $b=1$; (2) 单调递减区间为$(0,3-\sqrt{3})$和$(3+\sqrt{3},+\infty)$, 单调递增区间为$(-\infty, 0)$和$(3-\sqrt{3}, 3+\sqrt{3})$; (3) $3$个


18257
(1) $r_0=0$, $r_1=1$, $r_2=2$, $r_3=3$; (2) $r_n=n$($n \in \mathbf{N}$); (3) 证明略