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Prove that:(secθ - cosθ)(cotθ + tanθ) = tanθ.secθ.

Chapter 6 – Trigonometry – Text Book Solution

Practice Set 6.1| Q 6.4 | Page 132

Prove that:(secθ – cosθ)(cotθ + tanθ) = tanθ.secθ.

Solution To prove: $$(\sec\theta - \cos\theta)(\cot\theta + \tan\theta) = \tan\theta \sec\theta$$ We know that $$\cot\theta = \frac{\cos\theta}{\sin\theta}$$ and $$\tan\theta = \frac{\sin\theta}{\cos\theta}$$. Substituting these in the given equation, we get: $$(\sec\theta - \cos\theta)\left(\frac{\cos\theta}{\sin\theta} + \frac{\sin\theta}{\cos\theta}\right) = \frac{\sin\theta}{\cos\theta} \cdot \frac{1}{\cos\theta}$$ Multiplying both sides by $$\frac{\sin\theta \cos\theta}{\cos\theta}$$, we get: $$(\sec\theta - \cos\theta)(\cos^2\theta + \sin^2\theta) = \sin\theta$$ Using the identity $$\cos^2\theta + \sin^2\theta = 1$$, we get: $$(\sec\theta - \cos\theta) = \frac{\sin\theta}{1} = \sin\theta$$ Multiplying both sides by $$\frac{\cos\theta}{\sin\theta}$$, we get: $$(\sec\theta - \cos\theta)(\cot\theta + \tan\theta) = \tan\theta \sec\theta$$ Therefore, we have shown that $$(\sec\theta - \cos\theta)(\cot\theta + \tan\theta) = \tan\theta \sec\theta$$.

Solution

We can start by expanding the left-hand side of the equation using the definitions of secant, cosine, cotangent, and tangent:

(secθ – cosθ)(cotθ + tanθ)

= secθcotθ + secθtanθ – cosθcotθ – cosθtanθ

= (1/cosθ)(cosθ/sinθ) + (1/cosθ)(sinθ/cosθ) – cosθ*(cosθ/sinθ) – cosθ*(sinθ/cosθ)

= (1/sinθ) + (sinθ/cos²θ) – cos²θ/sinθ – sinθ

= [(1/cos²θ) – cos²θ]/sinθ + sinθ/cos²θ

= (1 – cos⁴θ)/sinθcos²θ + sinθ/cos²θ

= [(1 – cos²θ)(1 + cos²θ)]/sinθcos²θ

= (sin²θ/sinθ)(1/cos²θ)

= sinθ/cosθ

= tanθ.secθ

Therefore, we have shown that (secθ – cosθ)(cotθ + tanθ) = tanθ.secθ.

Explanation:- 

 

Chapter 6 – Trigonometry – Text Book Solution

Practice set 6.1 |Q 6.4 | P 132

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