1. Draw a sketch of the given straight line, the point D and the perpendicular line to AC.

2. The slope of the perpendicular line must be . Use the point-slope-formula:

3. The point B is the point of intersection between the given line and the perpendicular line:

Therefore the point B has the coordinates B(1, 5)

4. The point C has the coordinates C(2, 7) (You should now be able to explain how I got this result: Use the definition of slope and the equation of the given line)