We know that, #csc^2theta-cot^2theta=1.#
#:. (csctheta+cottheta)(csctheta-cottheta)=1.#
#:. (csctheta+cottheta)(1/sqrt3)=1...............[because," Given]."#
#:. csctheta+cottheta=sqrt3....................................................<<1>>.#
Also, #csctheta-cottheta=1/sqrt3......................[Given].............<<2>>.#
Then, #<<1>>+<<2>> rArr 2csctheta=sqrt3+1/sqrt3=4/sqrt3.#
#:. csc theta=2/sqrt3, &, <<1>> - <<2>>rArr cottheta=1/sqrt3.#
Hence, #costheta=costheta/sintheta*sintheta=cottheta*1/csctheta,#
#=1/sqrt3*sqrt3/2.#
# rArr costheta=1/2.#