$
(a) -\left(\dfrac{d^{2}y}{dx^{2}}\right)^{-1}\left(\dfrac{dy}{dx}\right)^{-3}
$
$ (b) \left(\dfrac{d^{2}y}{dx^{2}}\right)\left(\dfrac{dy}{dx}\right)^{-2}
$
$
(c) -\left(\dfrac{d^{2}y}{dx^{2}}\right)\left(\dfrac{dy}{dx}\right)^{-3}
$
$
(d) \left(\dfrac{d^{2}y}{dx^{2}}\right)^{-1}
$
. Find 
is
is
, then f(A)=
is
is
be the roots f the equation 
and 
are the roots of the equation 
, then the value of r,
, then the value of 
is
and 
are unit vectors, then 
does not exceeds
and 
and bisects the angle between 
and 
?