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Determinant Condition for Three Lines to Be Parallel
## Formula
For three lines:
$$A_ix+B_iy+C_i=0$$
they are parallel if:
$$\frac{A_1}{A_2}=\frac{B_1}{B_2}$$
and:
$$\frac{A_1}{A_3}=\frac{B_1}{B_3}$$
## Usage
- Used to verify that three lines have the same direction.
