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What do the markers mean on segments FC and ED?
m∠ 1=42^(∘)
m∠ 2=39^(∘)
m∠ 3=51^(∘)
For finding the different angles, let's focus on different parts of the figure.
In the right triangle △ FAB, the measure of one of the acute angles is given and we are asked to find the measure of the other acute angle.
To find the measure of ∠ 2, we can notice that FD is a transversal cutting lines FC and ED. Angles ∠ 2=∠ DFC and ∠ EDF are alternate interior angles.
The markers on segments FC and ED indicate that these segments are parallel. Thus, according to the Alternate Interior Angles Theorem, ∠ 2 and ∠ EDF are congruent, so their measures are the same. Since m∠ EDF=39 is given on the figure, this gives the measure of ∠ 2. m∠ 2=39^(∘)
Let's put the measure of ∠ 2=∠ DFC we just found on the diagram and focus on the right triangle △ CDF.