Write the equation of the straight line passing through the point C (1; 2; 4) and perpendicular to the OY axis.

Consider this point C (1; 2; 4). We can say about it that its x-coordinate is 1, the y-coordinate is 2, and the z-coordinate is 4.

Any straight line that is perpendicular to the OY axis will be parallel to the OX axis, it follows from this that the y coordinate in this case will be constant, and the x and z coordinates are all numbers. Therefore, the equation is written in the form y = const, where const = 2, so the equation has the form:

y = 3.

Answer: y = 3.