Class 10 Maths · Introduction to Trigonometry · NCERT Exercise 8.4 · Question 9

Introduction to Trigonometry Medium

tan θ + sec θ = l

, then prove that

sec θ = \frac{l ^{2} + 1}{2 l}

Answer

Adding

sec θ + tan θ = l

and

sec θ - tan θ = 1/ l

gives

2 sec θ = (l^{2} + 1) / l

, so

sec θ = (l^{2} + 1) / (2 l)

, as required.

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