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Geometry Difficulty 3.5 AMC 10/12 Find the answer

If the two sides of angle α\alpha and angle β\beta are parallel, and angle α\alpha is 3636^\circ less than three times angle β\beta, then the degree of angle α\alpha is ____.

A number or a short expression. Spacing and $ signs are ignored.

Solution

Given that the two sides of angle α\alpha and angle β\beta are parallel, we know that angle α\alpha and angle β\beta are either equal or supplementary. This is a key property of parallel lines intersected by a transversal.

Let's denote the measure of angle β\beta as xx^\circ. According to the problem, angle α\alpha is 3636^\circ less than three times angle β\beta. Therefore, we can express angle α\alpha as 3x363x^\circ - 36^\circ.

### Case 1: Angle α\alpha and angle β\beta are Equal
If angle α\alpha and angle β\beta are equal, we have:
x=3x36x = 3x - 36
Solving for xx, we rearrange the equation:
2x=362x = 36
x=18x = 18
Thus, if angle α\alpha and angle β\beta are equal, β=18\angle \beta = 18^\circ. Substituting x=18x = 18 into the expression for α\angle \alpha, we get:
α=3×1836=5436=18\angle \alpha = 3 \times 18^\circ - 36^\circ = 54^\circ - 36^\circ = 18^\circ

### Case 2: Angle α\alpha and angle β\beta are Supplementary
If angle α\alpha and angle β\beta are supplementary, their sum equals 180180^\circ. Therefore, we have:
x+3x36=180x + 3x - 36 = 180
Simplifying, we get:
4x=2164x = 216
x=54x = 54
Thus, if angle α\alpha and angle β\beta are supplementary, β=54\angle \beta = 54^\circ. Substituting x=54x = 54 into the expression for α\angle \alpha, we find:
α=3×5436=16236=126\angle \alpha = 3 \times 54^\circ - 36^\circ = 162^\circ - 36^\circ = 126^\circ

Therefore, the degree of angle α\alpha can be either 1818^\circ or 126126^\circ. Hence, the final answer is encapsulated as 18 or 126\boxed{18^\circ \text{ or } 126^\circ}.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.