In a $\triangle ABC$,if $\angle C = 90^{\circ}$,then $\frac{a^2-b^2}{a^2+b^2}$ is equal to

If $f(x) = x^3 - 10x^2 + 200x - 10$,then

Four charges equal to $-Q$ are placed at the four corners of a square and a charge $q$ is at its centre. If the system is in equilibrium,the value of $q$ is:

The sensitivity of a galvanometer is $60 \text{ division/A}$. When a shunt is used,its sensitivity becomes $10 \text{ division/A}$. If the galvanometer is of resistance $20 \ \Omega$,the value of shunt used is: (in $Omega$)

Match the following columns.

Column-$I$	Column-$II$
$A.$ $500$ million years ago	$1.$ Invertebrates
$B.$ $350$ million years ago	$2.$ Jawless fishes
$C.$ $320$ million years ago	$3.$ Sea weeds and few plants

$A$ physical quantity $X$ is given by $X = \frac{2 k^3 \ell^2}{m \sqrt{n}}$. The percentage errors in the measurement of $k, \ell, m,$ and $n$ are $1\%, 2\%, 3\%,$ and $4\%$ respectively. The percentage uncertainty in the value of $X$ is: (in $\%$)