The angle bisectors of angles $\beta$ and $\gamma$ in triangle $ABC$ form an angle $\varphi$. The ratio of the angles is given as $\alpha : \varphi = 1 : 2$ and $\beta : \gamma = 1 : 4$. We are asked to find the interior angles of the triangle.

GeometryTriangleAngle BisectorsAnglesSystem of Equations
2025/3/29

1. Problem Description

The angle bisectors of angles β\beta and γ\gamma in triangle ABCABC form an angle φ\varphi. The ratio of the angles is given as α:φ=1:2\alpha : \varphi = 1 : 2 and β:γ=1:4\beta : \gamma = 1 : 4. We are asked to find the interior angles of the triangle.

2. Solution Steps

Let the angles of the triangle be α\alpha, β\beta, and γ\gamma. We are given that β:γ=1:4\beta : \gamma = 1 : 4, so γ=4β\gamma = 4\beta. The sum of the angles in a triangle is 180180^{\circ}, so
α+β+γ=180\alpha + \beta + \gamma = 180^{\circ}.
Substituting γ=4β\gamma = 4\beta, we have
α+β+4β=180\alpha + \beta + 4\beta = 180^{\circ}
α+5β=180\alpha + 5\beta = 180^{\circ}.
Let the angle bisectors of β\beta and γ\gamma intersect at a point. Let φ\varphi be the angle between these angle bisectors.
The angle between the angle bisectors is given by
φ=180β2γ2=180β24β2=1805β2\varphi = 180^{\circ} - \frac{\beta}{2} - \frac{\gamma}{2} = 180^{\circ} - \frac{\beta}{2} - \frac{4\beta}{2} = 180^{\circ} - \frac{5\beta}{2}.
We are given that α:φ=1:2\alpha : \varphi = 1 : 2, so φ=2α\varphi = 2\alpha. Substituting this into the previous equation, we get
2α=1805β22\alpha = 180^{\circ} - \frac{5\beta}{2}.
4α=3605β4\alpha = 360^{\circ} - 5\beta.
4α+5β=3604\alpha + 5\beta = 360^{\circ}.
Now we have a system of two equations with two variables:
α+5β=180\alpha + 5\beta = 180^{\circ}
4α+5β=3604\alpha + 5\beta = 360^{\circ}
Subtracting the first equation from the second equation, we get
3α=1803\alpha = 180^{\circ}, so α=60\alpha = 60^{\circ}.
Substituting α=60\alpha = 60^{\circ} into the first equation, we get
60+5β=18060^{\circ} + 5\beta = 180^{\circ}
5β=1205\beta = 120^{\circ}
β=24\beta = 24^{\circ}.
Since γ=4β\gamma = 4\beta, we have γ=4(24)=96\gamma = 4(24^{\circ}) = 96^{\circ}.
So the angles are α=60\alpha = 60^{\circ}, β=24\beta = 24^{\circ}, and γ=96\gamma = 96^{\circ}.

3. Final Answer

α=60\alpha = 60^{\circ}, β=24\beta = 24^{\circ}, γ=96\gamma = 96^{\circ}.

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