Triangle Midsegment Theorem Theorem Theorem 6 2 Triangle Midsegment Theorem The segment connecting the midpoints of two sides of a triangle is parallel to the third side and is half as long as that side DE is a midsegment of LABC DE AC and DE AC A Proof Example 2 p 331 Monitoring Progress Question 3 p 331 Ex 22 p 334 DE is the midsegment of AABC Find the value of x A ERROR ANALYSIS Describe and correct the error X B 5 10 E C DE BC so by the Triangle Midsegment Theorem Thm 6 8 AD DB and AE EC