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If 3 cot θ = 4, find the value of 5 sin θ - 3 cos θ5 sin θ + 3 cos θ\dfrac{\text{5 sin θ - 3 cos θ}}{\text{5 sin θ + 3 cos θ}}.

Trigonometrical Ratios

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Answer

Given,

⇒ 3 cot θ = 4

⇒ cot θ = 43\dfrac{4}{3}

5 sin θ - 3 cos θ5 sin θ + 3 cos θ[Dividing numerator and denominator by sin θ](5 sin θ - 3 cos θ)sin θ(5 sin θ + 3 cos θ)sin θ5 sin θsin θ3 cos θsin θ5 sin θsin θ+3 cos θsin θ5 - 3 cot θ5+3 cot θ [cot θ=cos θsin θ]Substituting values we get53×435+3×43545+419.\dfrac{\text{5 sin θ - 3 cos θ}}{\text{5 sin θ + 3 cos θ}} \\[1em] [\text{Dividing numerator and denominator by sin θ}] \\[1em] \Rightarrow \dfrac{\dfrac{\text{(5 sin θ - 3 cos θ)}}{\text{sin θ}}}{\dfrac{\text{(5 sin θ + 3 cos θ)}}{\text{sin θ}}} \\[1em] \Rightarrow \dfrac{\dfrac{\text{5 sin θ}}{\text{sin θ}} - \dfrac{\text{3 cos θ}}{\text{sin θ}}}{\dfrac{\text{5 sin θ}}{\text{sin θ}} + \dfrac{\text{3 cos θ}}{\text{sin θ}}} \\[1em] \Rightarrow \dfrac{\text{5 - 3 cot θ}}{{5 + \text{3 cot θ}}} \space [\because \text{cot θ} = \dfrac{\text{cos θ}}{\text{sin θ}}] \\[1em] \text{Substituting values we get} \\[1em] \Rightarrow \dfrac{5 - 3 \times \dfrac{4}{3}}{5 + 3\times \dfrac{4}{3}} \\[1em] \Rightarrow \dfrac{5 - 4}{5 + 4} \\[1em] \Rightarrow \dfrac{1}{9}.

Hence, 5 sin θ - 3 cos θ5 sin θ + 3 cos θ=19\dfrac{\text{5 sin θ - 3 cos θ}}{\text{5 sin θ + 3 cos θ}} = \dfrac{1}{9}

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