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If 3 tan θ = 4, show that (3sinθ+2cosθ3sinθ2cosθ)\Big(\dfrac{3\sin θ + 2\cos θ}{3\sin θ - 2\cos θ}\Big)= 3.

Trigonometrical Ratios

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Answer

tan θ = perpendicularbase=43\dfrac{\text{perpendicular}}{\text{base}}=\dfrac{4}{3}

Let Perpendicular = 4x and Base = 3x

We will find hypotenuse by using pythagoras theorem

Hypotenuse2 = Perpendicular2 + Base2

Hypotenuse2 = (4x)2 + (3x)2

Hypotenuse2 = 16x2 + 9x2

Hypotenuse2 = 25x2

Hypotenuse = 5x

Now

sin θ = perpendicularhypotenuse=4x5x=45\dfrac{\text{perpendicular}}{\text{hypotenuse}}= \dfrac{4x}{5x} = \dfrac{4}{5}

cos θ = basehypotenuse=3x5x=35\dfrac{\text{base}}{\text{hypotenuse}}= \dfrac{3x}{5x} = \dfrac{3}{5}

Substituting values we get :

3 sin θ + 2 cos θ3 sin θ - 2 cos θ=3×45+2×353×452×35=125+6512565=12+651265=18565=18×55×6=186=3\Rightarrow \dfrac{\text{3 sin θ + 2 cos θ}}{\text{3 sin θ - 2 cos θ}} \\[1em] = \dfrac{3\times\dfrac{4}{5} + 2\times\dfrac{3}{5}}{3\times\dfrac{4}{5} -2\times\dfrac{3}{5}} \\[1em] = \dfrac{\dfrac{12}{5} + \dfrac{6}{5}}{\dfrac{12}{5} -\dfrac{6}{5}}\\[1em] = \dfrac{\dfrac{12+6}{5}}{\dfrac{12-6}{5}} \\[1em] = \dfrac{\dfrac{18}{5}}{\dfrac{6}{5}} \\[1em] = \dfrac{18\times5}{5\times6}\\[1em] = \dfrac{18}{6} = 3

Hence, proved that (3sinθ+2cosθ3sinθ2cosθ)\Big(\dfrac{3\sin θ + 2\cos θ}{3\sin θ - 2\cos θ}\Big) = 3.

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