If cosθ + sec θ = 10 , find the value of cos2θ + sec2θ .
Answer & explanation
Correct answer: option 2
Formula I → [ cosθ = \(\frac{1}{secθ}\)]
Formula II → [If x + \(\frac{1}{x}\) = n and x2 + \(\frac{1}{x^2}\) = n2 - 2]
cosθ + \(\frac{1}{cosθ}\) = 10
⇒ cos2θ + \(\frac{1}{cos^2θ}\) = (10)2 - 2
⇒ cos2θ + sec2θ = 100 - 2 = 98