Correct Answer - D

`tantheta=(1)/(sqrt(7))rArrcottheta=sqrt(7).`

`sec^(2)theta=(1+tan^(2)theta)=(1+(1)/(7))=(8)/(7)and "cosec"^(2)theta=(1+cot^(2)theta)=(1+7)=8.`

`therefore ("cosec"^(2)theta-sec^(2)theta)/("cosec"^(2)theta+sec^(2)theta)=((8-(8)/(7)))/((8+(8)/(7)))=(48)/(64)=(3)/(4).`