McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
1. Angles of Triangles
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Exercise 2 Page 339

What do the markers mean on segments FC and ED?

m∠ 1=42^(∘)
m∠ 2=39^(∘)
m∠ 3=51^(∘)

Practice makes perfect

For finding the different angles, let's focus on different parts of the figure.

Finding m∠ 1=m∠ FAB

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.

According to Corollary 4.1 of the Triangle Angle-Sum Theorem, the acute angles of a right triangle are complementary, so their measures add to 9^(∘).
m∠ FAB+m∠ ABF=90
m∠ FAB+ 48=90
m∠ FAB=42
The measure of ∠ 1=∠ FAB is 42^(∘).

Finding m∠ 2=m∠ DFC

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^(∘)

Finding m∠ 3=m∠ CDF

Let's put the measure of ∠ 2=∠ DFC we just found on the diagram and focus on the right triangle △ CDF.

As in finding m∠ 1, we can again use that acute angles of a right triangle are complementary to find m∠ 3.
m∠ CDF+m∠ DFC=90
m∠ CDF+ 39=90
m∠ CDF=51
The measure of ∠ 3=∠ CDF is 51^(∘).