Final answer:
To write an equation for a vertical translation, subtract the amount of the translation from the original equation. In this case, the equation y = 1/2x becomes y = 1/2x - 18, representing a vertical translation of 18 units downwards.
Step-by-step explanation:
To write an equation for the vertical translation, we start with the equation y = 1/2x. Since we need to shift the graph 18 units down, the equation becomes y = 1/2x - 18. This equation represents a vertical translation of 18 units downwards.