In the given figure,what do $A$ and $B$ represent respectively?

If $P_1, P_2, P_3$ are the perimeters of the three circles $x^2+y^2+8x-6y=0$,$4x^2+4y^2-4x-12y-186=0$,and $x^2+y^2-6x+6y-9=0$ respectively,then

Which of the following halides is the most stable?

$A$ particle at the end of a spring executes simple harmonic motion with a period $t_1$,while the corresponding period for another spring is $t_2$. If the period of oscillation with the two springs in series is $T$,then

Two identical thin bar magnets,each of length $l$ and pole strength $m$,are placed at a right angle to each other with the north pole of one touching the south pole of the other. The magnetic moment of the system is:

If $\frac{1}{x(x^2 + 1)} = \frac{A}{x} + \frac{Bx + C}{x^2 + 1}$,then $(A, B, C) = $