Trigonometry! #126

Geometry Level 3

If sin x a = cos x b = tan x c = k \frac{\sin x}{a}=\frac{\cos x}{b}=\frac{\tan x}{c}=k then b c + 1 c k + a k 1 + b k = ? bc+\frac{1}{ck}+\frac{ak}{1+bk}=?

This problem is part of the set Trigonometry .

1 k 2 \frac{1}{k^{2}} k ( a 1 a ) k\left(a-\frac{1}{a}\right) a k \frac{a}{k} 1 k ( a + 1 a ) \frac{1}{k}\left(a+\frac{1}{a}\right)

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1 solution

First we have that b c = cos ( x ) k tan ( x ) k = sin ( x ) k 2 = a k . bc = \dfrac{\cos(x)}{k}*\dfrac{\tan(x)}{k} = \dfrac{\sin(x)}{k^{2}} = \dfrac{a}{k}.

Next, 1 c k = 1 tan ( x ) = cos ( x ) sin ( x ) . \dfrac{1}{ck} = \dfrac{1}{\tan(x)} = \dfrac{\cos(x)}{\sin(x)}.

For the last term, we have a k 1 + b k = sin ( x ) 1 + cos ( x ) = 1 cos ( x ) sin ( x ) . \dfrac{ak}{1 + bk} = \dfrac{\sin(x)}{1 + \cos(x)} = \dfrac{1 - \cos(x)}{\sin(x)}.

Thus 1 c k + a k 1 + b k = 1 sin ( x ) = 1 a k , \dfrac{1}{ck} + \dfrac{ak}{1 + bk} = \dfrac{1}{\sin(x)} = \dfrac{1}{ak},

and so b c + 1 c k + a k 1 + b k = a k + 1 a k = 1 k ( a + 1 a ) . bc + \dfrac{1}{ck} + \dfrac{ak}{1 + bk} = \dfrac{a}{k} + \dfrac{1}{ak} = \boxed{\dfrac{1}{k}\left(a + \dfrac{1}{a}\right)}.

How did this question get into #Geometry when it clearly says TRIGONOMETRY!#126

Nit Jon - 6 years, 3 months ago

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When someone posts a question they are asked to classify it, and in this process of classification geometry is considered a main heading and trigonometry a subheading. Also, note that in the "Tagged with:" listing at the bottom of this page both #Geometry and #Trigonometry are tagged, (as well as #TrigonometricIdentities).

Brian Charlesworth - 6 years, 3 months ago

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Now it makes sense (thank you)!

Nit Jon - 6 years, 3 months ago

Geometry is the main topic, which covers a wide range of material

Calvin Lin Staff - 6 years, 3 months ago

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