McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
3. Inequalities in One Triangle
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Exercise 37 Page 431

Start by comparing RM and RP. Then compare RQ and RP.

RM > RQ

Practice makes perfect

In order to determine the relationship between RM and RQ, we can use Theorem 5.10 about Angle-Side Relationships in Triangles.

Angle-Side Relationships in Triangles

If one angle of a triangle has a greater measure than another angle, then the side opposite the greater angle is longer than the side opposite the lesser angle.

Note that this theorem is used to compare the sides of a triangle. For this reason, we will first compare the lengths of RM and RP, and the lengths of RQ and RP. Then, we will be able to determine the relationship between RM and RQ.

Relationship Between RM and RP

Let's highlight △ MPR.

We see that ∠ RPM is opposite to RM and ∠ PMR is opposite to RP. However, the diagram does not show a measure for ∠ RPM. To find this measure, we will first find m∠ MRP. Notice that ∠ SRM, ∠ MRP, and ∠ PRQ form a straight angle. The sum of their measures is 180^(∘). 60^(∘)+ m∠ MRP + 85^(∘) =180^(∘) ⇕ m∠ MRP =35^(∘)

Let's show this angle on the diagram.

Now, by the Triangle Angle Sum Theorem, we can find m∠ RPM.
m∠ PMR + m∠ MRP + m∠ RPM =180^(∘)
70^(∘)+ 35^(∘) + m∠ RPM =180^(∘)
Solve for m∠ MRP
105^(∘) + m∠ RPM =180^(∘)
m∠ RPM =75 ^(∘)
We can add this piece of information to the diagram.

Because ∠ RPM is greater than ∠ PMR, we know that RM is longer than RP. RM > RP

Relationship Between RQ and RP

Let's start by coloring △ QPR because RQ and RP are the sides of this triangle.

We will now find m∠ RQP using the Triangle Angle Sum Theorem. From the diagram, we know that m∠ QPR= 30^(∘) and m∠ PRQ= 85^(∘).
m∠ QPR + m∠ PRQ + m∠ RQP =180^(∘)
30^(∘)+ 85^(∘) + m∠ RQP =180^(∘)
Solve for m∠ RQP
115^(∘) + m∠ RQP =180^(∘)
m∠ RQP =65 ^(∘)
Let's put it on the diagram.

As we can see, ∠ RQP is opposite to RP and ∠ QPR is opposite to RQ. Therefore, since ∠ RQP is greater than ∠ QPR, we know that RP is longer than RQ. RP > RQ

Conclusion

We have shown the relationships between RM and RP, and RQ and RP. RM > RP RP > RQ Finally, we can use the Transitive Property to conclude that RM is greater than RQ. RM > RQ