Zhong Shupai sixth grade second semester math class exercises () Yanbian People's Publishing House) 7.2 Draw the sum, difference and times of line segments, the second big problem and the third small problem.
Solution: because point o is the midpoint of line segment AB, OB=a,
So AB = 2OB = 2a.
Because CD=b,
So AC+DB = AB-CD = 2A-B.
Because CE= 1/3AC, FB=2DF.
So CE+DF =1/3ac+1/3bd.
= 1/3(AC + BD)
= 1/3*(2a-b)
And EF=CE+DF+CD.
= 1/3*(2a-b)+b
=2/3a + 2/3b