If $\csc\theta + \cot\theta = 3$, then $\csc\theta - \cot\theta =$ ?
1/3
2/3
3
1
Correct answer: 1/3
Solution
Using $(\csc\theta+\cot\theta)(\csc\theta-\cot\theta)=\csc^2\theta-\cot^2\theta=1$. Since $\csc\theta+\cot\theta=3$, we get $3(\csc\theta-\cot\theta)=1$, so the required value is $1/3$.