Pearson Geometry Common Core, 2011
PG
Pearson Geometry Common Core, 2011 View details
5. Proportions in Triangles
Continue to next subchapter

Exercise 24 Page 475

Begin by sketching the triangle with its angle bisectors. Then, consider the Triangle-Angle-Bisector Theorem

See solution.

Practice makes perfect

Let's begin by sketching the triangle with its angle bisectors.

Considering the Triangle-Angle-Bisector Theorem, let's find the lengths of each pair of segments one at a time.

Lengths of BD and DC

We will first consider BD and DC.

By the theorem, we can write a proportion for BD and DC. AB/AC=BD/DC We have already been given AB=5 and AC=12. In this case, to find BD and DC, we should identify a relation between them. Knowing that BC=13 and considering the Segment Addition Postulate, let's write DC in terms of BD. BC=BD+DC ⇓ DC= 13-BD Next, we will substitute the given values and DC=13-BD into the proportion, so we can find the length of BD.
AB/AC=BD/DC
5/12=BD/13-BD
Solve for BD
5(13-BD)=12BD
65-5BD=12BD
65=17BD
65/17=BD
BD=65/17
BD=3.82352...
BD≈3.8
Now, we can find DC by substituting BD≈ 3.8 into DC=13-BD.
DC=13-BD
DC=13- 3.8
DC≈ 9.2

Lengths of AE and EC

As our second pair of segments, we will think of AE and EC.

Considering the Triangle-Angle-Bisector Theorem, let's write a proportion to find AE and EC. AB/BC=AE/EC Next, we will rewrite EC in terms of AE using the fact that AC=12. AC=AE+EC ⇓ EC= 12-AE Now, we will first find AE by substituting the value into the proportion.
AB/BC=AE/EC
5/13=AE/12-AE
Solve for AE
5(12-AE)=13AE
60-5AE=13AE
60=18AE
60/18=AE
10/3=AE
AE=10/3
AE=3.33333...
AE≈ 3.3
Now that we know AE, we can find EC as well.
EC=12-AE
EC=12- 3.3
EC≈ 8.7

Lengths of AF and FB

Finally, we will find AF and FB.

For AF and FB, we can write the following proportion. AC/BC=AF/FB Next, we will again rewrite FB in terms of AF given that AB=5. AB=AF+FB ⇓ FB= 5-AF Now, let's find AF.
AC/BC=AF/FB
12/13=AF/5-AF
Solve for AF
12(5-AF)=13AF
60-12AF=13AF
60=25AF
60/25=AF
12/5=AF
AF=12/5
AF=2.4
We have found that AF=2.4. From here, we can also find FB.
FB=5-AF
FB=5-2.4
FB=2.6