Integer tangents?

Geometry Level 4

We know the tangents of the angles α , β , γ \alpha, \beta, \gamma of a triangle are positive integers.

Compute:

tan ( α ) + tan ( β ) + tan ( γ ) . \tan(\alpha) + \tan(\beta) + \tan(\gamma) .


The answer is 6.

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1 solution

Utsav Banerjee
Apr 22, 2015

From property of triangles, we know that

t a n ( α ) + t a n ( β ) + t a n ( γ ) = t a n ( α ) t a n ( β ) t a n ( γ ) tan(\alpha)+tan(\beta)+tan(\gamma)=tan(\alpha)tan(\beta)tan(\gamma)

Let t a n ( α ) = n 1 tan(\alpha)=n_{1} , t a n ( β ) = n 2 tan(\beta)=n_{2} , and t a n ( γ ) = n 3 tan(\gamma)=n_{3} , where n 1 n_{1} , n 2 n_{2} & n 3 n_{3} are positive integers.

Therefore, n 1 + n 2 + n 3 = n 1 n 2 n 3 n_{1}+n_{2}+n_{3}=n_{1}n_{2}n_{3} , which has only one solution ( 1 , 2 , 3 ) (1,2,3) . Hence, t a n ( α ) + t a n ( β ) + t a n ( γ ) = 6 tan(\alpha)+tan(\beta)+tan(\gamma)=6 .

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