Since m is that midpoint of BC and e is the midpoint of AC, ME= 1/2AB,
Connect EN Since n is the midpoint of AD, NE is parallel to CD, and NE= 1/2CD.
Because the straight line AB makes an angle of 60 with CD, and the straight line ME makes an angle of 60 with ne.
And AB=CD, ME= 1/2AB, NE= 1/2CD.
Therefore, if the line segment ME=NE, the triangle MNE is an isosceles triangle and the angle MEN is 60,
Then the angle EMN =1/2 (180-60) = 60, and ME is parallel to AB, so the angle formed by straight line AB and MN is also 60.