McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
5. Parts of Similar Triangles
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Exercise 33 Page 589

Create a system of equations using the Triangle Angle Bisector Theorem.

PS≈18.4 , RS≈ 24

Practice makes perfect

Let's begin with recalling the Triangle Angle Bisector Theorem. An angle bisector in a triangle separates the opposite side into two segments that are proportional to the lengths of the other two sides. Now let's look at the given picture. Let x be the length of PS and y be the length of SR.

Since QS is an angle bisector of ∠ Q, we can write a proportion. x/y=22.4/29.2 We also know that the perimeter of this triangle is 94 units. Let's use this information to write a second equation. Recall that a perimeter is a sum of all side lengths. 22.4+29.2+( x+ y)= 94 Let's create a system of equations using the two equations we found above. xy= 22.429.2 & (I) 22.4+29.2+(x+y)=94 & (II) First, we can simplify them a little bit before using the Substitution Method.
xy= 22.429.2 & (I) 22.4+29.2+(x+y)=94 & (II)
(I), (II):Simplify
x*29.2=y*22.4 22.4+29.2+(x+y)=94
29.2x=22.4y 22.4+29.2+(x+y)=94
29.2x=22.4y 22.4+29.2+x+y=94
29.2x=22.4y 51.6+x+y=94
29.2x=22.4y x+y=42.4
29.2x=22.4y x=42.4-y
Since we isolated x in the second equation, we can solve this system using the Substitution Method. To do this, let's substitute 42.4-y for x in the first equation.
29.2x=22.4y x=42.4-y
29.2( 42.4-y)=22.4y x=42.4-y
(I):Solve for y
29.2(42.4)+29.2(- y)=22.4y x=42.4-y
1238.08-29.2y=22.4y x=42.4-y
1238.08=51.6y x=42.4-y
51.6y=1238.08 x=42.4-y
y=23.9937... x=42.4-y
y≈24 x=42.4-y
The value of y is approximately 24 units. By substituting this value into the second equation, we will find the approximate value of x.
y≈24 x=42.4-y
y≈24 x≈42.4- 24
y≈24 x≈18.4
The value of x is approximately 18.4. Therefore, the length of PS is about 18.4 units and the length of SR is about 24 units.