If $l_1 \parallel l_2$, find the sizes of the angles $\alpha$, $\beta$ and $\gamma$ in the following diagram - Junior Cycle Mathematics - Question 11 - 2013
Question 11
If $l_1 \parallel l_2$, find the sizes of the angles $\alpha$, $\beta$ and $\gamma$ in the following diagram.

Worked Solution & Example Answer:If $l_1 \parallel l_2$, find the sizes of the angles $\alpha$, $\beta$ and $\gamma$ in the following diagram - Junior Cycle Mathematics - Question 11 - 2013
Step 1
Find $\alpha$
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Answer
We consider the triangle with angles 73∘, 60∘, and 2α. The sum of these three angles is 180∘:
2α+73+60=180
This simplifies to:
2α=180−73−60=47
Thus,
α=247=23.5∘
Step 2
Find $\beta$
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Answer
Next, we consider the triangle with angles α, β, and 73∘. Again, the sum of these angles is 180∘:
73+α+β=180
Substituting the value of α we calculated:
73+23.5+β=180
This simplifies to:
β=180−73−23.5=83.5∘
Step 3
Find $\gamma$
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Answer
Finally, since the two lines are parallel, corresponding angles are equal. Therefore:
γ=α=23.5∘
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