Consider the following series:

(i) $\sum\limits_{n=1}^{\infty} \frac{1}{\sqrt{n}}$

(ii) $ \sum\limits_{n=1}^{\infty} \frac{1}{n(n+1)}$

(iii) $\sum\limits_{n=1}^{\infty} \frac{1}{n!}$

Consider the function $f: \mathbb{R} \rightarrow \mathbb{R}$ defined as

$$ f(x)=2 x^3-3 x^2-12 x+1 $$

Which of the following statements is/are correct?

(Here, $\mathbb{R}$ is the set of real numbers.)

Consider the two-dimensional vector field $$\overrightarrow F (x,y) - x\overrightarrow i + y\overrightarrow j $$, where $$\overrightarrow i $$ and $$\widehat j$$ denote the unit vectors along the x-axis and the y-axis, respectively. A contour C in the x-y plane, as shown in the figure, is composed of two horizontal lines connected at the two ends by two semicircular arcs of unit radius. The contour is traversed in the counter-clockwise sense. The value of the closed path integral

$$\oint\limits_C {\overrightarrow F (x,y)\,.\,(dx\overrightarrow i + dy\overrightarrow j )} $$

is ___________.

The families of curves represented by the solution of the equation

$${{dy} \over {dx}} = - {\left( {{x \over y}} \right)^n}$$

for n = –1 and n = 1 respectively, are