Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
5. Angle Relationships in Circles
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Exercise 13 Page 566

Start with calculating the measure of MP and the central angle that intercepts it. Then use the Circumscribed Angle Theorem.

x=34

Practice makes perfect

We are given the following diagram and asked to find the value of x.

From the diagram we can see that ∠ L intercepts arc MP. By the Measure of an Inscribed Angle Theorem, this means the measure of ∠ L is half the measure of MP. m∠ L=1/2mMPLet's substitute m∠ L with 73^(∘) and find the value of mMP.
m∠ L=1/2mMP
73^(∘)=1/2mMP
146^(∘)=mMP
mMP=146^(∘)
Now we can find the measure of the central angle ∠ MOP, which intercepts arc MP.

Let's recall that the measure of a central angle is equal to the measure of its intercepted arc. Therefore, the measure of ∠ MOP is also 146^(∘). m∠ MOP=146^(∘) From the diagram, we can also see that the sides of ∠ N are tangent to the circle, so ∠ N is a circumscribed angle. We can use the Circumscribed Angle Theorem, which states the following.

Circumscribed Angle Theorem

The measure of a circumscribed angle is equal to 180^(∘) minus the measure of the central angle that intercepts the same arc.

The circumscribed angle ∠ N and the central angle ∠ MOP intercept the same arc MP, so the following is true. m∠ N=180^(∘)-m∠ MOP Let's substitute m∠ N with x^(∘) and m∠ MOP with 146^(∘) to find the value of x.
m∠ N=180^(∘)-m∠ MOP
x^(∘)=180^(∘)- 146^(∘)
x^(∘)=34^(∘)
We conclude that the value of x is 34.