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If α is a root of 25 cos2 θ + 5 cos θ – 12 = 0, π/2 < α < π, then sin 2α is equal to

(A) \(-\frac{24}{25}\)

(B) \(-\frac{13}{18}\)

(C) \(\frac{13}{18}\)

(D) \(\frac{24}{25}\)

1 Answer

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Best answer

Correct answer is (A) \(-\frac{24}{25}\)

25 cos2 θ + 5 cos θ – 12 = 0

∴ (5cos θ + 4) (5 cos θ – 3) = 0

∴ cos θ = \(-\frac{4}{5}\) or cos θ = \(\frac{3}{5}\)

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