`~rai~`
\(b)y=\tan|x|\\+)ĐKXĐ:\cos|x|\ne 0\\\Leftrightarrow |x|\ne\dfrac{\pi}{2}+k\pi\\\Leftrightarrow x\ne\pm\dfrac{\pi}{2}+k\pi.\\\Rightarrow D=\mathbb{R}\backslash\left\{\pm\dfrac{\pi}{2}+k\pi\Big|k\in\mathbb{Z}\right\}.\\\Rightarrow \forall x\in D\quad thì\quad -x\in D.(1)\\+)f(-x)=\tan|-x|\\\quad\quad\quad\quad=\tan|x|\\\quad\quad\quad\quad=f(x).\quad(2)\\\text{Từ (1) và (2)}\Rightarrow \text{f(x) là hàm số chẵn.}\\c)y=\dfrac{\sin x-\tan x}{\sin x+\tan x}\\+)ĐKXĐ:\begin{cases}\cos x\ne 0\\\sin x+\tan x\ne 0\end{cases}\\\Leftrightarrow \begin{cases}x\ne\dfrac{\pi}{2}+k\pi\\\sin x+\dfrac{\sin x}{\cos x}\ne 0\end{cases}\\\Leftrightarrow \begin{cases}x\ne\dfrac{\pi}{2}+k\pi\\\sin x\cos x+\sin x\ne 0\end{cases}\\\Leftrightarrow \begin{cases}x\ne\dfrac{\pi}{2}+k\pi\\\sin x(\cos x+1)\ne 0\end{cases}\\\Leftrightarrow \begin{cases}x\ne\dfrac{\pi}{2}+k\pi\\\sin x\ne 0\\\cos x\ne -1\end{cases}\\\Leftrightarrow \begin{cases}x\ne\dfrac{\pi}{2}+k\pi\\x\ne k\pi\\x\ne \pi+k2\pi\end{cases}\\\Leftrightarrow x\ne k\dfrac{\pi}{2}.(k\in\mathbb{Z})\\\Rightarrow D=\mathbb{R}\backslash\left\{k\dfrac{\pi}{2}\Big|k\in\mathbb{Z}\right\}\\\Rightarrow \forall x\in D\quad thì\quad -x\in D.(1)\\+)f(-x)=\dfrac{\sin(-x)-\tan(-x)}{\sin(-x)+\tan(-x)}\\\quad\quad\quad\quad=\dfrac{-\sin x+\tan x}{-\sin x-\tan x}\\\quad\quad\quad\quad=\dfrac{-(\sin x-\tan x)}{-(\sin x+\tan x)}\\\quad\quad\quad\quad=\dfrac{\sin x-\tan x}{\sin x+\tan x}\\\quad\quad\quad\quad=f(x).\quad(2)\\\text{Từ (1) và (2)}\Rightarrow \text{f(x) là hàm số chẵn.}\)
