Construction- parallel lines
Constructing the parallel to (CB) passing through A.
1. Using the set square, draw the straight line passing through A and perpendicular to (CB) at H. 2. Using the set square, draw the straight line (DE) passing through A and perpendicular to (AH). The two straight lines (CB) and (AH), being perpendicular to the same straight line (AH), are parallel. (DE) is then the required straight line.