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Mathematics

(sec θ - cos θ)2 - (sec θ + cos θ)2 is equal to :

  1. 4

  2. 2

  3. -2

  4. -4

Trigonometric Identities

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Answer

Solving,

⇒ (sec θ - cos θ)2 - (sec θ + cos θ)2

⇒ (sec θ - cos θ + sec θ + cos θ)[(sec θ - cos θ) - (sec θ + cos θ)] [∵ a2 - b2 = (a + b)(a - b)]

⇒ (sec θ - cos θ + sec θ + cos θ)(sec θ - sec θ - cos θ - cos θ)

⇒ 2 sec θ.(-2 cos θ)

⇒ -4.sec θ.cos θ

4×1cos θ×cos θ-4 \times \dfrac{1}{\text{cos θ}} \times \text{cos θ}

⇒ -4.

Hence, Option 4 is the correct option.

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