The equation ${\sec ^2}\theta = \frac{{4xy}}{{{{(x + y)}^2}}}$ is only possible when
$x = y$
$x < y$
$x > y$
None of these
Find the radian measures corresponding to the following degree measures:
$240^{\circ}$
If $x = a{\cos ^3}\theta ,y = b{\sin ^3}\theta ,$ then
If $\tan \theta = \frac{{20}}{{21}},$ cos$\theta$ will be
Prove that: $\frac{(\sin 7 x+\sin 5 x)+(\sin 9 x+\sin 3 x)}{(\cos 7 x+\cos 5 x)+(\cos 9 x+\cos 3 x)}=\tan 6 x$
Find the value of $\cos \left(-1710^{\circ}\right)$.