1, AB is the maximum slope line to the H plane, and AB must be perpendicular to the intersection line (horizontal line) between this plane and the H plane.

2. On the front, the horizontal line a'c' passes through A', and on the H plane, the vertical line ac ab.

3, abc is the desired plane.

Second, draw a positive line 25 mm away from the V plane.

1, h plane, make a straight line at a distance of 25mm from the O-X axis, and cross ab, ac, M, N.

2, v plane, find m' and n'

draw

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