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Mathematics

If 13 sin θ = 5, find the value of

5 sin θ - 2 cos θtan θ\dfrac{\text{5 sin θ - 2 cos θ}}{\text{tan θ}}

Trigonometrical Ratios

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Answer

13 sin θ = 5

sin θ = 513\dfrac{5}{13}

sin θ = perpendicularhypotenuse=513\dfrac{\text{perpendicular}}{\text{hypotenuse}} =\dfrac{\text{5}}{\text{13}}

Let perpendicular = 5x and hypotenuse = 13x

By pythagoras theorem, we get :

Hypotenuse2 = Base2 + Perpendicular2

Base2 = Hypotenuse2 - Perpendicular2

Base2 = (13x)2 - (5x)2

Base2 = 169x2 - 25x2

Base2 = 144x2

Base = 144x2\sqrt{144x^2}

Base = 12x

cos θ = basehypotenuse=12x13x=1213\dfrac{\text{base}}{\text{hypotenuse}} = \dfrac{12x}{13x} = \dfrac{12}{13}

tan θ = perpendicularbase=5x12x=512\dfrac{\text{perpendicular}}{\text{base}} = \dfrac{5x}{12x} = \dfrac{5}{12}

Substituting values, we get :

5 sin θ - 2 cos θtan θ=5×5132×1213512=25132413512=113512=1265.\Rightarrow \dfrac{\text{5 sin θ - 2 cos θ}}{\text{tan θ}} = \dfrac{5 \times \dfrac{5}{13} - 2 \times \dfrac{12}{13}}{\dfrac{5}{12}} \\[1em] = \dfrac{\dfrac{25}{13} - \dfrac{24}{13}}{\dfrac{5}{12}} \\[1em] = \dfrac{\dfrac{1}{13}}{\dfrac{5}{12}} \\[1em] = \dfrac{12}{65}.

Hence, 5 sin θ - 2 cos θtan θ=1265\dfrac{\text{5 sin θ - 2 cos θ}}{\text{tan θ}} = \dfrac{12}{65}.

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