Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
Chapter Review
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Exercise 6 Page 342

Use the Midpoint Formula to find the midpoints.

See solution.

Practice makes perfect

We will first draw △ ABC using the given vertices A(0,0), B(2,2), and C(5,-1).

Now, we will find L, the midpoint of AC by using the Midpoint Formula. Notice that the endpoints of AC are A( 0, 0) and C( 5, -1).
L(x_1+x_2/2,y_1+y_2/2)
L(0+ 5/2,0+( -1)/2)
Simplify
L(5/2,-1/2)
L(2.5,-0.5)

We have found the coordinates of L as (2.5,-0.5). We can find M, the midpoint of BC, in the same way.

L (x_1+x_2/2,y_1+y_2/2) A&( 0, 0) C&( 5, -1) (0+ 5/2,0+( -1)/2) L(2.5, -0.5)
M (x_1+x_2/2,y_1+y_2/2) B&( 2, 2) C&( 5, -1) (2+ 5/2,2+( -1)/2) M(3.5, 0.5)

The coordinates of M are (3.5,0.5). Let's place the midpoints on the triangle and draw LM.

The slopes of the parallel lines are the same. Therefore, to verify that AB∥ML, we will use the Slope Formula to show that their slope are the same. Let's start with the slope of AB, m_1. Notice that the endpoints of AB are A( 0, 0) and B( 2, 2).
m_1=y_2-y_1/x_2-x_1
m_1=2- 0/2- 0
m_1=2/2
m_1=1
The slope of AB is 1. Using the same way, we can find the slope of ML, m_2.
m_1 m_1=y_2-y_1/x_2-x_1 A&( 0, 0) B&( 2, 2) m_1=2- 0/2- 0 m_1=1
m_2 m_2=y_2-y_1/x_2-x_1 M&( 3.5, 0.5) L&( 2.5, -0.5) m_2=-0.5- 0.5/2.5- 3.5 m_2=1
As a result, both AB and ML have the same slope, so they are parallel. Next, we will verify that LM= 12AB by finding AB and LM. Therefore, we will use the Distance Formula. Let's first find AB.
AB=sqrt((x_2-x_1)^2+(y_2-y_1)^2)
AB=sqrt(( 2- 0)^2+( 2- 0)^2)
AB=sqrt(2^2+2^2)
AB=sqrt(4+4)
AB=sqrt(8)
AB=sqrt(4*2)
AB=sqrt(4)*sqrt(2)
AB=2sqrt(2)
The length of AB is 2sqrt(2). Next, we will find LM, using the same method.
AB AB=sqrt((x_2-x_1)^2+(y_2-y_1)^2) A&( 0, 0) B&( 2, 2) AB=sqrt(( 2- 0)^2+( 2- 0)^2) AB=2sqrt(2)
LM LM=sqrt((x_2-x_1)^2+(y_2-y_1)^2) L&( 2.5, -0.5) M&( 3.5, 0.5) LM=sqrt(( 3.5- 2.5)^2+( 0.5- -0.5)^2) LM=sqrt(2)
Now that we have also found the length of LM, we can compare their lengths.
LM=1/2AB
sqrt(2)? =1/2( 2sqrt(2))
sqrt(2)=sqrt(2)
At the end, we have an identity. Thus, we have also verified that LM= 12AB.