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Find sinθ such that 3cosθ + 4sinθ = 4 - Mathematics and Statistics

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प्रश्न

Find sinθ such that 3cosθ + 4sinθ = 4

बेरीज

उत्तर

3cosθ + 4 sinθ = 4

∴ 3cosθ = 4 – 4sinθ

∴ 3cosθ = 4(1 – sinθ)

Squaring both the sides, we get,

9cos2θ = 16(1 – sinθ)2

∴ 9(1 – sin2θ) = 16(1 + sin2θ – 2sinθ)

∴ 9 – 9sin2θ = 16 + 16sin2θ – 32sinθ

∴ 25sin2θ – 32sinθ + 7 = 0

∴ 25sin2θ – 25sinθ – 7sinθ + 7 = 0

∴ 25sinθ (sinθ – 1) – 7(sinθ – 1) = 0

∴ (sinθ – 1)(25sinθ – 7) = 0

∴ sinθ – 1 = 0 or 25sinθ – 7 = 0

∴ sinθ = 1 or sinθ = `7/25`

Since, – 1 ≤ sinθ ≤ 1

∴ sinθ = 1 or `7/25`

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Fundamental Identities
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पाठ 2: Trigonometry - 1 - EXERCISE 2.2 [पृष्ठ ३१]

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