4.( 1) (3,0) ; Perpendicular to each other (drawing: coordinates A 1 (3,0), B2 (1,1), C2 (1, 0))

(2)( 1,- 1)

5.( 1) Connect AA 1, CC 1, intersection point A and A 1, draw an arc with a compass with the length of AA 1 as the radius, and connect.

These two points draw a straight line (and the middle vertical line of AA 1), and so does CC 1. Then two straight lines intersect at one point, which is D.

②54 and 234.

If you have any ambiguity or questions, please point them out! )

Pure hand tour, hope to adopt! ! ! ! ! ! ! ! ! !