What is the condition for two linear graphs to be parallel and perpendicular to each other?

Okay, thanyaninebonde, let's continue with these questions.

3.1.3:
From the graphs chosen in 2.2.1, we have $y=2x$ and $y=2x+1$. Both of these graphs have a gradient of 2. When two linear graphs have the same gradient, they are parallel to each other.

The two graphs are parallel to each other.

$$\boxed{\text{parallel}}$$

3.1.4:
This question refers to the condition for two linear graphs to be perpendicular.

Conclusion: If the product of the two gradients of two linear graphs is equal to $\boxed{-1}$, therefore the linear graphs are $\boxed{\text{perpendicular}}$ to each other.