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Geometry Level 2

If 3 cot θ = 5 3\cot\theta = 5 , then find the value of

5 sin θ 3 cos θ 5 sin θ + 3 cos θ \dfrac{5\sin \theta-3\cos \theta}{5\sin \theta+3\cos \theta}

3 5 \dfrac{3}{5} 0 0 5 4 \dfrac{5}{4} 4 5 \dfrac{4}{5} 5 3 \dfrac{5}{3}

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2 solutions

Ayush G Rai
Sep 11, 2016

3 c o t θ = 5. 3cot\theta=5. So 3 c o s θ s i n θ = 5 3 c o s θ = 5 s i n θ . \dfrac{3cos\theta}{sin\theta}=5\Rightarrow 3cos\theta=5sin\theta.
Substitute this in the question, 5 s i n θ 3 c o s θ 5 s i n θ + 3 c o s θ = 5 s i n θ 5 s i n θ 5 s i n θ + 5 s i n θ = 0 . \dfrac{5sin\theta-3cos\theta}{5sin\theta+3cos\theta}=\dfrac{5sin\theta-5sin\theta}{5sin\theta+5sin\theta}=\boxed 0.

Viki Zeta
Sep 10, 2016

3 cot θ = 5 5 sin θ 3 cos θ 5 sin θ + 3 cos θ = 5 sin θ 3 cos θ sin θ 5 sin θ + 3 cos θ sin θ = 5 3 cot θ 5 + 3 cot θ = 5 5 5 + 5 = 0 10 = 0 3\cot\theta = 5 \\ \dfrac{5\sin\theta-3\cos\theta}{5\sin\theta+3\cos\theta} = \dfrac{\dfrac{5\sin\theta-3\cos\theta}{\sin\theta}}{\dfrac{5\sin\theta+3\cos\theta}{\sin\theta}} \\ = \dfrac{5 - 3\cot\theta}{5 + 3\cot\theta} \\ = \dfrac{5 - 5}{5 + 5} = \dfrac{0}{10} = 0

Since sin \sin and cos \cos are functions like ln \ln (\ln), \sqrt{} (\sqrt ), \int (\int) and lim \lim (\lim). you should put a backslash in front sin \sin (\sin) and cos \cos (\cos). Note that they are not italic which is for valuables such as x , y , z , d x , d y , d z , θ x, y, z, dx, dy, dz, \theta . Note that they are italic like in your solution without the backslash s i n sin (sin) and c o s cos (cos).

Chew-Seong Cheong - 4 years, 9 months ago

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Ok. will follow it from next time

Viki Zeta - 4 years, 9 months ago

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I have done the changes for your solution above.

Chew-Seong Cheong - 4 years, 9 months ago

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@Chew-Seong Cheong Thank you!

Viki Zeta - 4 years, 9 months ago

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