Consider the function $f(x) = x \cos x - \sin x$. Identify the correct statement.

If $y=(x+1)(x^2+1)(x^4+1)(x^8+1)$,then $\lim _{x \rightarrow-1} \frac{dy}{dx}=$

Let $k$ and $m$ be positive real numbers such that the function $f(x) = \begin{cases} 3x^2 + k\sqrt{x+1}, & 0 < x < 1 \\ mx^2 + k^2, & x \geq 1 \end{cases}$ is differentiable for all $x > 0$. Then $\frac{8f'(8)}{f'(\frac{1}{8})}$ is equal to $.............$.

For any positive integer $n$,define $f_n:(0, \infty) \rightarrow R$ as $f_n(x)=\sum_{j=1}^n \tan ^{-1}\left(\frac{1}{1+(x+j)(x+j-1)}\right)$ for all $x \in(0, \infty)$. Then,which of the following statement$(s)$ is (are) $TRUE$?
$(A)$ $\sum_{j=1}^5 \tan ^2(f_j(0))=55$
$(B)$ $\sum_{j=1}^{10}(1+f_j'(0)) \sec ^2(f_j(0))=10$
$(C)$ For any fixed positive integer $n$,$\lim _{x \rightarrow \infty} \tan (f_n(x))=\frac{1}{n}$
$(D)$ For any fixed positive integer $n$,$\lim _{x \rightarrow \infty} \sec ^2(f_n(x))=1$

Let $f(x)$ be a non-negative differentiable function on $[0, \infty)$ such that $f(0)=0$ and $f^{\prime}(x) \leq 2 f(x)$ for all $x>0$. Then,on $[0, \infty)$:

Let $f(x) = \begin{cases} x^{3/5} & \text{if } x \le 1 \\ -(x - 2)^3 & \text{if } x > 1 \end{cases}$. Then the number of critical points on the graph of the function is: