Point, line and surface problems in high school mathematics]]

The intersection m, which is a line parallel to AB, passes through AC and point E,

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.