0606 P21 - Nov 2024 - Q1 - 3 marks
7239
Show that \(\tan \theta+\cot \theta\) can be written as \(\sec \theta \operatorname{cosec} \theta\).
Solution
Answer: \(\tan\theta+\cot\theta=\sec\theta\operatorname{cosec}\theta\).
Use the standard trigonometric identities and make sure the final angles are chosen from the interval given in the question.
Write each term using sine and cosine:
\(\tan\theta+\cot\theta=\frac{\sin\theta}{\cos\theta}+\frac{\cos\theta}{\sin\theta}.\)
Using a common denominator,
\(\frac{\sin^2\theta+\cos^2\theta}{\sin\theta\cos\theta}=\frac{1}{\sin\theta\cos\theta}.\)
Since \(\sec\theta=\frac{1}{\cos\theta}\) and \(\operatorname{cosec}\theta=\frac{1}{\sin\theta}\),
\(\frac{1}{\sin\theta\cos\theta}=\sec\theta\operatorname{cosec}\theta.\)
This gives the required answer: \(\tan\theta+\cot\theta=\sec\theta\operatorname{cosec}\theta\).