ABCD is a trapezium such that AB and CD are parallel
and `B C_|_C D`
. If `/_A D B""=theta,""B C""=""p""a n d""C D""=""q`
, then AB is
equal to
(1) `(p^2+q^2costheta)/(pcostheta+qsintheta)`
(2) `(p^2+q^2)/(p^2costheta+q^2sintheta)`
(3) `((p^2+q^2)sintheta)/((pcostheta+qsintheta)^2)`
(4) `((p^2+q^2)sintheta)/(pcostheta+qsintheta)`