Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
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Exercise 3 Page 587

m∠1=29^(∘), m∠2=66^(∘), m∠3=37^(∘)

Practice makes perfect

Consider the given diagram.

We will find the measures of ∠1, ∠2, and ∠3 one at a time.

Finding ∠1

Looking at the diagram, we can see that ∠1 is formed by the intersection of two secants outside the circle. In this case, we can consider the Angles Outside the Circle Theorem.

Angles Outside the Circle Theorem

If a tangent and a secant, two tangents, or two secants intersect outside a circle, then the measure of the angle formed is one-half the difference of the measures of the intercepted arcs.

We can see that the measures of the intercepted arcs are 96^(∘) and 38^(∘).

With this information, we can find the measure of ∠1.
m∠1=96^(∘)-38^(∘)/2
m∠ 1 = 58^(∘)/2
m∠ 1 = 29 ^(∘)

Finding ∠2

Looking at the diagram, we can see that ∠2 is formed by the intersection of two chords inside the circle. In this case, we can consider the Angles Inside the Circle Theorem.

Angles Inside the Circle Theorem

If two chords intersect inside a circle, then the measure of the angle formed is one-half the sum of the measures of the arcs intercepted by the angle and its vertical angle.

We can see that the measures of the intercepted arcs are 96^(∘) and 36^(∘).

With this information, we can find the measure of ∠2.
m∠2=96^(∘)+36^(∘)/2
m∠ 2 = 132^(∘)/2
m∠ 2 = 66^(∘)

Finding ∠3

Note that the angle ∠3 is an inscribed angle and the measure of its intercepted arc is given. In this case, we can consider using the Inscribed Angle Theorem.

Inscribed Angle Theorem

The measure of an inscribed angle is one-half the measure of its intercepted arc.

With this in mind, we can find the measure of ∠3 in the given diagram.

Noticing that the measure of the intercepted arc is the sum of 36^(∘) and 38^(∘), we can calculate the measure of ∠3.
m∠3=36^(∘)+38^(∘)/2
m∠ 3 = 74^(∘)/2
m∠ 3 = 37 ^(∘)