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    Question

    If P . cos θ + Q . sin θ = 8 and P . sin θ - Q . cos

    θ = 5, what is the value of (P² + Q²)?
    A 89 Correct Answer Incorrect Answer
    B 40 Correct Answer Incorrect Answer
    C 13 Correct Answer Incorrect Answer
    D 2√10 Correct Answer Incorrect Answer

    Solution

    Given, P . cos θ + Q . sin θ = 8 ⇒ P² . cos² θ + Q² . sin² θ + 2PQ . sin θ . cos θ = 64   … (i) Also given, P . sin θ - Q . cos θ = 5 ⇒ P² . sin² θ + Q² . cos² θ - 2PQ . sin θ . cos θ = 25   … (ii) Adding equations (i) and (ii) P² + Q² = 89

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