Theorem:
In a triangle, if a segment joins the midpoints of two sides, then it is parallel to the third side, and half the length of the third side.
In each of the triangles in the figures above, the side of the large triangle is twice the length of the segment inside the triangle.
1.
DB = 2RS
x + 27 = 2(x + 17)
x + 27 = 2x + 34
-x = 7
x = -7
DB = x + 27 = -7 + 27 = 20
Answer: DB = 20
2.
TR = 2CD
x + 26 = 2(x + 17)
x + 26 = 2x + 34
-x = 8
x = -8
TR = x + 26 = -8 + 26 = 18
Answer: TR = 18
3.
UW = 2SR
x + 10 = 2(x + 8)
x + 10 = 2x + 16
-x = 6
x = -6
SR = x + 8 = -6 + 8 = 2
Answer: SR = 2
